Include Orbit REST API endpoints in OpenAPI spec

What does this MR do and why?

Update Orbit API endpoints to manually documented in https://docs.gitlab.com/api/orbit/ to be automatically included in doc/api/openapi/openapi_v3.yaml. Set x-gitlab-lifecycle to beta for Orbit API endpoints. Use orbit tag for Orbit API endpoints.

References

• Publish Orbit and Artifact Registry REST APIs i... (gitlab-org/quality#428 - closed)
• Generate Orbit API specs and publish it in the ... (#619525 - closed)
• Add response schemas to Orbit's Grape endpoints (#624037)

Screenshots or screen recordings

How to set up and validate locally

1. Confirm 6 public Orbit API endpoints manually documented in doc/api/orbit.md are included in doc/api/openapi/openapi_v3.yaml.

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