[HTTP/OAS] Add descriptions for Logstash pipeline APIs

[lcawl]

Summary

Relates to #180056

This PR adds operation summaries for the Logstash configuration management APIs in the generated OpenAPI document.

NOTE: I've omitted the "access: public" from the "delete pipelines" and "get all pipelines" operations, since those don't currently exist in the documentation. I believe this means they'll use the default "internal" access value.

How to test

Per #181277:

1. Start Elasticsearch (e.g. yarn es snapshot --license trial)
2. Add server.oas.enabled: true to kibana.dev.yml
3. Start Kibana (e.g. yarn start --no-base-path)
4. curl -s -u elastic http://localhost:5601/api/oas\?pathStartsWith\=/api/logstash/pipeline | jq > test.json

The output will contain info like this:

   "paths": {
    "/api/logstash/pipeline/{id}": {
      "delete": {
        "summary": "Delete a Logstash pipeline",

[apmmachine]

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[karenzone]

I left some suggestions inline for consideration. Do we have a character limit? The fact that these APIs work only for centrally-managed Logstash pipelines is significant.

[lcawl]

Do we have a character limit? The fact that these APIs work only for centrally-managed Logstash pipelines is significant.

Yes, this is the "operation summary" which is used as the title in the navigation bar, so we've added a linting rule to limit its length. Originally we were linting for strings to be less than 30, though I've updated that now to go as much as 45.

If all of these APIs apply to the same type of pipeline, it would be my preference to cover that either at the group level (in a "tag" description) or in the API detailed description and leave these nav titles as short as they are in the existing docs.
The functionality to add tag descriptions and detailed operation descriptions are currently outstanding per #182649 and #182779

It's also worth calling out that our guidelines for these summaries is that they "use common verbs like Get, Update, Delete whenever possible" so the suggested changes to "Retrieve" and "List" would fail a linting rule too.

[karenzone]

Thanks for explaining the constraints. I modified my comments to use standard terminology and to respect the character limit... assuming that only display text counts against character limits. :-) Please LMKWYT

[karenzone]

LGTM (pending passing ci). :-) Thanks for your work on this, @lcawl

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