Create release status when finalizing monthly release

What does this MR do and why?

For issue gitlab-com/gl-infra/delivery#20022 (closed)

Creates a new delivery_release_monthly_status metric for the next minor version when finalizing a monthly release.

• release_monthly_status
  • The metric value corresponds to the release status:
    • Open (1): Engineers can create MRs, and any commit that reached production is expected to be released with the next monthly release
    • Announced (2): Signals the RC tagging date is getting closer
    • Tagged (3): Final RC has been tagged, any commit that has not reached production prior to the tagging time is not included in the monthly release)
  • labels:
    • version
    • release_date
• Feature flag: release_monthly_status_metric