[Feature flag] Cleanup `vsa_standalone_settings_page`

Summary

This issue is to cleanup the vsa_standalone_settings_page feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production. It productizes the settings pages for Value Stream Analytics at both the group and project levels.

Owners

• Team: groupoptimize
• Most appropriate slack channel to reach out to: #g_plan_optimize
• Best individual to reach out to: @rcrespo3 @blabuschagne
• PM: @hsnir1

Expectations

What might happen if this goes wrong?

• Inability to edit/create value streams
• We'd probably need to rollback any MRs related to both the rollout and the cleanup of this feature flag

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.