Feature flag rollout: mr_default_title_template

Summary

Rollout issue for the mr_default_title_template feature flag (beta).

This feature allows project maintainers to configure a default merge request title template at the project level, supporting variables like %{source_branch}, %{target_branch}, %{title_from_branch}, %{issue_title}, %{first_commit}, and %{first_multiline_commit}.

Feature MR: !228442 (closed) Feature issue: #16080 Feature flag type: beta

Rollout Steps

Enablement

• Enable on staging (/chatops run feature set mr_default_title_template true --staging)
• Test on staging
• Enable on GitLab.com for a percentage of projects
• Monitor error rates and performance
• Enable on GitLab.com globally (/chatops run feature set mr_default_title_template true)

Cleanup

• Remove feature flag from code
• Remove feature flag YAML definition
• Remove feature flag gating from BuildService, settings view, and specs
• Add changelog entry