Refine ADR: API Design

Context

The API design ADR needs refinement to ensure proper Cells routing compatibility, particularly with the /o/{org_id} URL pattern requirement.

Tasks

• [ ] Check proper Cells routing compatibility
• [ ] Ensure /o/{org_id} URL pattern is implemented
• Document API endpoints and routing strategy
• Validate API design with Tenant Scale team
• Complete and merge ADR
• Update that /v2/ challenge response is no longer necessary. See https://gitlab.com/gitlab-org/gitlab/-/work_items/595150#container-clients-docker-podman-buildah-skopeo-crane.
• Update the ADR given that local cache entries are no longer in scope. See gitlab-com/content-sites/handbook!19487 (merged).
• NPM missing routes: gitlab-org/ops/artifact-registry!98 (comment 3298683845)
• NPM audit route: gitlab-org/ops/artifact-registry!98 (diffs)A941

Related

• Parent Epic: &20959
• ADR MR: !18458
• Split Blueprint Issue: #590282 (closed)
• Tenant Scale Meeting Notes: https://gitlab.com/gitlab-org/gitlab/-/issues/589257#note_3075916483