Credit caps page for flat and per-user credit caps

This issue is the public record for the GitLab 19.4 release note. Implementation was tracked in internal issues.

GitLab Credits caps can now be configured in the product on the new Credit caps page, instead of only through the GraphQL API. You can set the flat cap that applies to every user by default, and add per-user overrides for individual users through a searchable picker.

On GitLab.com, group Owners find the page under Settings > GitLab Credits. On GitLab Self-Managed, instance administrators find it under Admin > GitLab Credits. The upsertFlatUserCap and upsertUserBudgetCapOverrides GraphQL mutations continue to work for scripted cap changes.

Shipped in GitLab 19.4. Documentation: https://docs.gitlab.com/subscriptions/gitlab_credits_dashboard/#set-flat-user-cap-and-per-user-overrides