[Feature Flag] Enable wiki events

What

Remove the :wiki_events feature flag, and enable wiki event recording by default

Owners

• Team: groupknowledge
• Most appropriate slack channel to reach out to: #g_create_knowledge
• Best individual to reach out to: Alex Kalderimis @akalderimis

Expectations

### What are we expecting to happen?

Once enabled, this will enable activity about wiki events to be recorded by default, and they will appear in the activity feeds.

What might happen if this goes wrong?

Performance impact is possible, which should be monitored for. Also, we need to watch for runtime errors in the activity APIs

What can we monitor to detect problems with this?

Monitoring ProjectsController#activity

Roll Out Steps

• Enable on staging
• Test on staging
• Ensure that documentation has been updated
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour
• Coordinate a time to enable the flag with #production and #g_delivery on slack.
• Announce on the issue an estimated time this will be enabled on GitLab.com
• Enable on GitLab.com by running chatops command in #production
• Cross post chatops slack command to #support_gitlab-com 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