[Ingest Pipelines] Fixes processors description (elastic#193183)

## Summary

Fixes elastic#191530 

This PR adds a stringify helper that is safe to use with objects,
arrays, text and numbers. `set` and `append` processors are using this
new helper to display `value` in the processor description. Other type
of processors don't seem to need it. This PR fixes the pipeline page so
that other processors in the pipeline still can be edited via UI.
This PR however doesn't fix the processors forms: both processors
currently can't handle json objects when editing. This should be fix in
a [separate issue](elastic#193186).

### Screenshots 
<img width="586" alt="Screenshot 2024-09-17 at 16 54 18"
src="https://github.com/user-attachments/assets/e1eb64a3-975c-4db7-98a5-b872ec1b016d">
<img width="586" alt="Screenshot 2024-09-17 at 16 54 34"
src="https://github.com/user-attachments/assets/ac57406f-ff22-461e-b788-6bdb2d18d7e9">

### How to test

Use this commands in Console to create processors with a json in
`value`.

```
PUT _ingest/pipeline/test2
{
  "processors": [
    {
          "set" : {
            "field" : "payload",
            "value" : "test",
            "if" : "ctx.payload == \"-\""
          }
    }
  ]
}


PUT _ingest/pipeline/test1
{
  "processors": [
    {
      "append": {
        "field": "test",
        "value": {
          "redacted": true
        }
      }
    }
  ]
}
```

### Checklist

Delete any items that are not applicable to this PR.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] Any UI touched in this PR is usable by keyboard only (learn more
about [keyboard accessibility](https://webaim.org/techniques/keyboard/))
- [ ] Any UI touched in this PR does not create any new axe failures
(run axe in browser:
[FF](https://addons.mozilla.org/en-US/firefox/addon/axe-devtools/),
[Chrome](https://chrome.google.com/webstore/detail/axe-web-accessibility-tes/lhdoppojpmngadmnindnejefpokejbdd?hl=en-US))
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This renders correctly on smaller devices using a responsive
layout. (You can test this [in your
browser](https://www.browserstack.com/guide/responsive-testing-on-local-server))
- [ ] This was checked for [cross-browser
compatibility](https://www.elastic.co/support/matrix#matrix_browsers)


### Risk Matrix

Delete this section if it is not applicable to this PR.

Before closing this PR, invite QA, stakeholders, and other developers to
identify risks that should be tested prior to the change/feature
release.

When forming the risk matrix, consider some of the following examples
and how they may potentially impact the change:

| Risk | Probability | Severity | Mitigation/Notes |

|---------------------------|-------------|----------|-------------------------|
| Multiple Spaces&mdash;unexpected behavior in non-default Kibana Space.
| Low | High | Integration tests will verify that all features are still
supported in non-default Kibana Space and when user switches between
spaces. |
| Multiple nodes&mdash;Elasticsearch polling might have race conditions
when multiple Kibana nodes are polling for the same tasks. | High | Low
| Tasks are idempotent, so executing them multiple times will not result
in logical error, but will degrade performance. To test for this case we
add plenty of unit tests around this logic and document manual testing
procedure. |
| Code should gracefully handle cases when feature X or plugin Y are
disabled. | Medium | High | Unit tests will verify that any feature flag
or plugin combination still results in our service operational. |
| [See more potential risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx) |


### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

x-pack/plugins/ingest_pipelines/public/application/components/pipeline_editor/__jest__/pipeline_processors_editor.test.tsx

@@ -395,4 +395,39 @@ describe('Pipeline Editor', () => {
       assertTestProcessor({ description: processorDescriptions.none, descriptionVisible: false });
     });
   });
+
+  describe('object values', () => {
+    const mockData: Pick<Pipeline, 'processors'> = {
+      processors: [
+        {
+          set: {
+            field: 'test',
+            value: { test: 'test' },
+          },
+        },
+        {
+          append: {
+            field: 'test',
+            value: { test: 'test' },
+          },
+        },
+      ],
+    };
+    it('editor works when value is an object', async () => {
+      onUpdate = jest.fn();
+      testBed = await setup({
+        value: {
+          ...mockData,
+        },
+        onFlyoutOpen: jest.fn(),
+        onUpdate,
+      });
+      expect(testBed.find(`processors>0.inlineTextInputNonEditableText`).text()).toBe(
+        'Sets value of "test" to "{"test":"test"}"'
+      );
+      expect(testBed.find(`processors>1.inlineTextInputNonEditableText`).text()).toBe(
+        'Appends "{"test":"test"}" to the "test" field'
+      );
+    });
+  });
 });

x-pack/plugins/ingest_pipelines/public/application/components/pipeline_editor/components/shared/map_processor_type_to_form.tsx

@@ -10,6 +10,7 @@ import React, { ReactNode } from 'react';
 import { FormattedMessage } from '@kbn/i18n-react';
 import { EuiCode, EuiLink } from '@elastic/eui';
 
+import { stringifyValueDescription } from './stringify_value_description';
 import { LicenseType } from '../../../../../types';
 
 import {
@@ -127,7 +128,7 @@ export const mapProcessorTypeToDescriptor: MapProcessorTypeToDescriptor = {
         defaultMessage: 'Appends "{value}" to the "{field}" field',
         values: {
           field,
-          value,
+          value: stringifyValueDescription(value),
         },
       }),
   },
@@ -810,7 +811,7 @@ export const mapProcessorTypeToDescriptor: MapProcessorTypeToDescriptor = {
         defaultMessage: 'Sets value of "{field}" to "{value}"',
         values: {
           field,
-          value,
+          value: stringifyValueDescription(value),
         },
       });
     },

x-pack/plugins/ingest_pipelines/public/application/components/pipeline_editor/components/shared/stringify_value_description.test.ts

@@ -0,0 +1,29 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { stringifyValueDescription } from './stringify_value_description';
+
+describe('StringifyValueDescription', () => {
+  it('works for a json object', () => {
+    expect(stringifyValueDescription({ test: 'test' })).toEqual('{"test":"test"}');
+  });
+  it('works for an array', () => {
+    expect(stringifyValueDescription(['a', 'b'])).toEqual('["a","b"]');
+  });
+  it('works for a string', () => {
+    expect(stringifyValueDescription('test')).toEqual('test');
+  });
+  it('works for a number', () => {
+    expect(stringifyValueDescription(123)).toEqual('123');
+  });
+  it('empty string for undefined', () => {
+    expect(stringifyValueDescription(undefined)).toEqual('');
+  });
+  it('empty string for null', () => {
+    expect(stringifyValueDescription(null)).toEqual('');
+  });
+});

x-pack/plugins/ingest_pipelines/public/application/components/pipeline_editor/components/shared/stringify_value_description.ts

@@ -0,0 +1,22 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+export const stringifyValueDescription = (value: unknown): string => {
+  if (!value) {
+    return '';
+  }
+  if (typeof value === 'object') {
+    try {
+      // if the value is a json object, it will be stringified as json
+      return JSON.stringify(value);
+    } catch (e) {
+      // ignore any errors
+    }
+  }
+  // otherwise just return a stringified value
+  return String(value);
+};