[HTTP] Make case APIs public

[lcawl]

Summary

Relates to #180056, #137240

This PR mirrors #183945 to make the same changes for the case APIs.

NOTE: The openAPI output currently contains the following endpoint for which we don't have docs:
/api/cases/{case_id}/resolve. It seems related to #110854. TBD whether it ought to be included in the public docs

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 -uelastic:changeme http://localhost:5601/api/oas\?pathStartsWith\=/api/cases | jq > test.json

The output will contain summaries like this:

  "paths": {
    "/api/cases": {
      "delete": {
        "summary": "Delete a case",
        "requestBody": {

[apmmachine]

🤖 GitHub comments

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Just comment with:

• /oblt-deploy : Deploy a Kibana instance using the Observability test environments.
• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[elasticmachine]

Pinging @elastic/response-ops-cases (Feature:Cases)

[cnasikas]

LGTM! I left some comments.

[kibana-ci]

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• Commit: 0b5644b

Metrics [docs]

✅ unchanged

History

• 💛 Build #212445 was flaky 3a6200c

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