[Cases] Case action: Error handling and retries (#173012)

## Summary

This PR:

1. Creates the `CasesConnectorError` error
2. Separate the execution logic by moving the current logic to a new
class called `CasesConnectorExecutor`
3. Let the `CasesConnector` class handle only the retry logic of the
connector
4. Implements the [Full jitter backoff
algorithm](https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/)
which is used as the retry strategy of the connector

Depends on: #172709

### Checklist

Delete any items that are not applicable to this PR.

- [x] [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

### For maintainers

- [x] 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)

---------

Co-authored-by: kibanamachine <[email protected]>

x-pack/plugins/cases/server/connectors/cases/cases_connector_error.ts

@@ -0,0 +1,24 @@
+/*
+ * 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 { CaseError } from '../../common/error';
+
+export class CasesConnectorError extends Error {
+  public readonly statusCode: number;
+
+  constructor(message: string, statusCode: number) {
+    super(message);
+
+    this.statusCode = statusCode;
+  }
+}
+
+export const isCasesConnectorError = (error: unknown): error is CasesConnectorError =>
+  error instanceof CasesConnectorError;
+
+export const isCasesClientError = (error: unknown): error is CaseError =>
+  error instanceof CaseError;