[ResponseOps][PerUserAuth] Add API availability docs to OAuth callback routes

[jcger]

Summary

Closes #257715

Adds availability: { since: '9.4.0' } to the two public OAuth routes introduced in #252369 (OAuth 2.0 Authorization Code Grant):

• GET /api/actions/connector/_oauth_callback
• GET /api/actions/connector/_oauth_callback_script

This ensures the generated API docs show "Added in 9.4" for both serverless and stack (non-serverless) documentation.

The two internal routes (_start_oauth_flow, _oauth_disconnect) don't need this annotation — the framework only applies availability to public routes, and internal routes are excluded from the OAS output.

[elasticmachine]

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

[florent-leborgne]

LGTM for docs, thanks for adding this!

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 4ea3da2

Failed CI Steps

• FTR Configs #84
• FTR Configs #119
• FTR Configs #130
• FTR Configs #204

Test Failures

• [job] [logs] FTR Configs #130 / Detections Response - Detection rule type telemetry @ess @serverless Detection rule status telemetry "eql" rule type should have non zero values for "index_duration"
• [job] [logs] FTR Configs #204 / Endpoint plugin @ess @serverless @skipInServerlessMKI Endpoint policy response api GET /api/endpoint/policy_response "before all" hook for "should return one policy response for an id"

Metrics [docs]

✅ unchanged

[kibanamachine]

Starting backport for target branches: 9.5

https://github.com/elastic/kibana/actions/runs/24233530658

[kibanamachine]

💔 All backports failed

Status	Branch	Result
❌	9.5	The branch "9.5" does not exist

Manual backport

To create the backport manually run:

node scripts/backport --pr 262292

Questions ?

Please refer to the Backport tool documentation