Adds documentation for 'Automatically disable Auto DevOps for project upon first pipeline failure'

What does this MR do?

Adds documentation for Automatically disable Auto DevOps for project upon first pipeline failure and for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21503

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• Documentation created/updated
• [-] Tests added for this feature/bug
• [-] Conforms to the code review guidelines
• [-] Conforms to the merge request performance guidelines
• [-] Conforms to the style guides
• [-] Conforms to the database guides