Rollout: auto_assign_code_owner_reviewers feature flag
## Summary
Feature flag rollout issue for `auto_assign_code_owner_reviewers`.
This feature flag gates the automatic assignment of CODEOWNERS as reviewers on merge requests.
## Feature flag
- **Name:** `auto_assign_code_owner_reviewers`
- **Type:** `gitlab_com_derisk`
- **Default:** `false`
- **Group:** `group::code review`
## Related
- Epic: https://gitlab.com/groups/gitlab-org/-/epics/20708
- Design issue: https://gitlab.com/gitlab-org/gitlab/-/issues/589700
- Implementation MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/223240
## Rollout plan
- [ ] Enable on staging
- [ ] Enable on gitlab.com for a subset of projects
- [ ] Monitor for errors/performance issues
- [ ] Enable on gitlab.com globally
- [ ] Remove feature flag and clean up
issue