Update feature flag name for Cycle Analytics

See merge request gitlab-org/gitlab-ce!32641

(cherry picked from commit 76c0af29)

3e55012f Update feature flag name for Cycle Analytics

Evan Read authored 5 years ago and Achilleas Pipinellis committed 5 years ago

Also fixes links to new section and refactors some existing content
for the GitLab 12.2 changes.