[Feature flag] Cleanup of `include_manual_to_pipeline_completion`

Summary

This issue is to cleanup the include_manual_to_pipeline_completion feature flag, as the feature flag has been enabled by default for more than 2 weeks. See: #440652 (comment 1795284971)

Note: Also as part of cleanup address the concerns captured in #440652 (comment 1775579751)

This feature has been in production and so the flag is being cleaned up but the feature will remain.

Owners

• Team: groupthreat insights
• Most appropriate slack channel to reach out to: #g_TEAM_NAME
• Best individual to reach out to: @bala.kumar
• PM: NAME

Stakeholders

Expectations

What might happen if this goes wrong?

Cleaning up the feature flag

• Specify in the issue description if this feature will be removed completely or will be productized as part of the Feature Flag cleanup
• Create a merge request to remove <feature-flag-name> feature flag. Ask for review and merge it.
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
  • Create a changelog entry.
• Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post.
  • /chatops run auto_deploy status <merge-commit-of-cleanup-mr>
• Close the feature issue to indicate the feature will be released in the current milestone.
• If not already done, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops run feature delete <feature-flag-name> --dev --pre --staging --staging-ref --production
• Close this rollout issue.