Add chatops implementation for checking if specific MRs are in a given package

What does this MR do and why?

Describe in detail what your merge request does and why.

This merge request adds a new feature that allows teams to check whether specific merge requests have been included in a specific auto-deploy package version.

The change works by taking a normalized package version (ex: 18.5.202510150007) and a list of merge request URLs, then automatically verifying if those changes made it into that specific package. It can detect changes that were included directly or through cherry-picking.

When the check completes, it sends a Slack notification with a summary showing which merge requests were successfully included and which ones weren't, along with any errors encountered during the process. This helps teams quickly verify that important fixes or features are present in a release without manually searching through code history.

The feature is accessible through chatops and includes comprehensive error handling to deal with cases like unmerged requests, unknown projects, or API failures.

Related issue: gitlab-com/gl-infra/delivery#21583

Author Check-list

• Has documentation been updated?

Testing

• (please check this thread for detailed testing)
• Test scenarios
  • Direct Inclusion - MR Merged to Auto-Deploy Branch
  • Cherry-Picked Inclusion - MR Cherry-Picked to the Security Branch
  • Not Included - MR Not in Package
  • Multiple MRs - Mixed Results
  • Error Handling - Unmerged MR
  • Error Handling - Unknown Project
  • Error Handling - Non-existent Package Version
  • With MR from other managed projects
  • With MR from security projects