[ML] Script to generate a content page for the ML Kibana API (#154538)

## Summary

- Adds a script to generate a content page with ML Kibana API groups
- Updates the `apiDocs` npm command

x-pack/plugins/ml/.gitignore

@@ -1,3 +1,4 @@
 scripts/apidoc_scripts/ML_API.mdx
+scripts/apidoc_scripts/ml_kibana_api.mdx
 scripts/apidoc_scripts/header.md
 apidoc_config.json

x-pack/plugins/ml/package.json

@@ -7,6 +7,7 @@
   "scripts": {
     "generateHeader": "node scripts/apidoc_scripts/header_generator/index.js",
     "generateApidocConfig": "node scripts/apidoc_scripts/apidoc_config/index.js",
-    "apiDocs": "yarn generateHeader && yarn generateApidocConfig && cd ./scripts/apidoc_scripts/ && ../../../../../node_modules/.bin/apidoc-markdown -i ../../server/routes -c ./apidoc_config.json -o ./ML_API.mdx --parse-workers apischema=./schema_worker/index.js --parse-parsers apischema=./schema_parser/index.js --parse-filters apiversion=./version_filter/index.js --header ./header.md --template ./template.md"
+    "generateContentPage": "node scripts/apidoc_scripts/content_page/index.js",
+    "apiDocs": "yarn generateContentPage && yarn generateHeader && yarn generateApidocConfig && cd ./scripts/apidoc_scripts/ && ../../../../../node_modules/.bin/apidoc-markdown -i ../../server/routes -c ./apidoc_config.json -o ./ML_API.mdx --parse-workers apischema=./schema_worker/index.js --parse-parsers apischema=./schema_parser/index.js --parse-filters apiversion=./version_filter/index.js --header ./header.md --template ./template.md"
   }
-}
+}

x-pack/plugins/ml/scripts/apidoc_scripts/content_page/content_page.ts

@@ -0,0 +1,68 @@
+/*
+ * 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 * as fs from 'fs';
+import * as path from 'path';
+// @ts-ignore can only be default-imported using the 'esModuleInterop' flag
+import moment from 'moment';
+import { kibanaPackageJson } from '@kbn/repo-info';
+// eslint-disable-next-line import/no-extraneous-dependencies
+import { createDoc } from 'apidoc-light';
+
+interface Group {
+  anchor: string;
+  text: string;
+}
+
+const getContent = (groups: Group[]) => {
+  const groupsStr = groups
+    .map(({ anchor, text }) => `- <DocLink id="uiMlApi" section="${anchor}" text="${text} API" />`)
+    .join('\n');
+
+  return `---
+  id: uiMlKibanaRestApi
+  slug: /ml-team/docs/ui/rest-api/ml-kibana-rest-api
+  title: Machine Learning Kibana REST API
+  image: https://source.unsplash.com/400x175/?Nature
+  description: This page contains documentation for the ML Kibana REST API.
+  date: ${moment().format('YYYY-MM-DD')}
+  tags: ['machine learning','internal docs', 'UI']
+  ---
+
+  _Updated for ${kibanaPackageJson.version}_
+
+  Some of the features of the Machine Learning (ML) Kibana plugin are provided via a REST API, which is ideal for creating an integration with the ML plugin.
+
+  Each API is experimental and can include breaking changes in any version of the ML plugin, or might have been entirely removed from the plugin.
+
+  - <DocLink id="uiMlApi" text="View complete API documentation" />
+
+  The following APIs are available:
+
+${groupsStr}
+  `;
+};
+
+export const generateContentPage = () => {
+  const doc = createDoc({
+    src: path.resolve(__dirname, '..', '..', '..', 'server', 'routes'),
+    config: path.resolve(__dirname, '..', 'apidoc_config', 'apidoc.json'),
+    // if you don't want to generate the output files:
+    dryRun: true,
+    // if you don't want to see any log output:
+    silent: true,
+  });
+
+  const groups = [...new Set(doc.data.map((v) => v.group))].map((group) => {
+    return {
+      anchor: `-${group.toLowerCase()}`,
+      text: group.replace(/([a-z])([A-Z])/g, '$1 $2'),
+    };
+  });
+
+  fs.writeFileSync(path.resolve(__dirname, '..', 'ml_kibana_api.mdx'), getContent(groups));
+};

x-pack/plugins/ml/scripts/apidoc_scripts/content_page/index.js

@@ -0,0 +1,9 @@
+/*
+ * 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.
+ */
+
+require('../../../../../../src/setup_node_env');
+require('./content_page').generateContentPage();