chore: add new JSDoc endpoint check rule

[MattDevy]

I would advise viewing this PR per-commit, as commit 2 is pretty large!

---

Commits:

1. Adds the eslint rule to validate the JSDocs of endpoints
   a. Includes a fixer
2. Runs npm run lint --prefix specification -- --fix to fix existing JSDocs that violate the rules outlined in JSDoc endpoint comments should be explicitly split in summary and description #2757

---

Example output:

npm run lint --prefix specification -- --fix

> specification@0.1.0 lint
> eslint --fix


/Users/mdevy/Documents/Github/elasticsearch-specification/specification/_global/bulk/BulkRequest.ts
   51:1  error  Markdown error (MD040/fenced-code-language): Fenced code blocks should have a language specified  es-spec-validator/jsdoc-endpoint-check
   90:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  102:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  107:1  error  Markdown error (MD040/fenced-code-language): Fenced code blocks should have a language specified  es-spec-validator/jsdoc-endpoint-check
  115:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  120:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  126:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  133:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  137:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check

/Users/mdevy/Documents/Github/elasticsearch-specification/specification/_global/create/CreateRequest.ts
  47:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading  es-spec-validator/jsdoc-endpoint-check
  67:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading  es-spec-validator/jsdoc-endpoint-check
  78:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading  es-spec-validator/jsdoc-endpoint-check
  83:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading  es-spec-validator/jsdoc-endpoint-check

/Users/mdevy/Documents/Github/elasticsearch-specification/specification/_global/delete/DeleteRequest.ts
  42:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  47:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  55:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check
  63:1  error  Markdown error (MD040/fenced-code-language): Fenced code blocks should have a language specified  es-spec-validator/jsdoc-endpoint-check
  70:1  error  Markdown error (MD036/no-emphasis-as-heading): Emphasis used instead of a heading                 es-spec-validator/jsdoc-endpoint-check

// ...

✖ 219 problems (219 errors, 0 warnings)

---

Outstanding Questions

1. What do we do about the existing markdown errors within the JSDocs?
2. Which branches will need this backporting?

[github-actions]

Following you can find the validation changes against the target branch for the APIs.

No changes detected.

You can validate these APIs yourself by using the make validate target.

[MattDevy]

@pquentin given this makes changes to the docs (added spaces), does this need backporting to 9.2, 9.1 and 8.19?