backport of custom metrics for the common metrics section of CE

What does this MR do?

Backport of the common metrics from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3799

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Frontend

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3799