[Feature flag] Rollout of `vue_issue_header`

What

Remove the :vue_issue_header feature flag. This feature flag toggles between the issue header showing various action buttons (off) and showing an ellipsis dropdown with actions in the dropdown menu.

Related to #233974 (closed)

Owners

• Team: groupproject management
• Most appropriate slack channel to reach out to: #s_plan
• Best individual to reach out to: @cngo

Expectations

What are we expecting to happen?

What might happen if this goes wrong?

What can we monitor to detect problems with this?

Beta groups/projects

Roll Out Steps

• Enable on staging (/chatops run feature set feature_name true --staging)
• Test on staging
• Ensure that documentation has been updated
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour (/chatops run feature set --project=gitlab-org/gitlab feature_name true)
• Coordinate a time to enable the flag with the SRE oncall and release managers
  • In #production by pinging @sre-oncall
  • In #g_delivery by pinging @release-managers
• Announce on the issue an estimated time this will be enabled on GitLab.com
• Enable on GitLab.com by running chatops command in #production (/chatops run feature set feature_name true)
• Cross post chatops Slack command to #support_gitlab-com (more guidance when this is necessary in the dev docs) and in your team channel
• Announce on the issue that the flag has been enabled
• Remove feature flag and add changelog entry
• After the flag removal is deployed, clean up the feature flag by running chatops command in #production channel

Rollback Steps

• This feature can be disabled by running the following Chatops command:

/chatops run feature set --project=gitlab-org/gitlab vue_issue_header false