Support alerting for dashboard yml-defined metrics (all chart types)

Problem to solve

Users should be able to set alerts on metrics defined in dashboard yml files in the project. The ability is available for gitlab-defined "common" metrics & custom metrics created in the UI, but not yet for yml-defined metrics. https://gitlab.com/gitlab-org/gitlab-ce/issues/60905 should introduce support for all metrics displayed as area-chart, but other chart types may have different needs & should be considered independently.

• Open questions:
  • Do the queries & alerts for other chart types line up with format for area-charts?
    • Ex) do we alert on heat maps? What does that look like?
  • How might the alerting UI be different for alternate chart types?

Intended users

Further details

Proposal

Permissions and Security

Documentation

Testing

What does success look like, and how can we measure that?

Links / references