[Backend] Support the ability to know why a group of charts have no data

Backend Issue for #30135

Problem to solve

Right now, we don't have very granular error messages on charts - we simply say 'no data to display' if there is any error in displaying the charts.

To improve this messaging, it would be good to figure out how to get more granular information about why the chart display is failing, for example: group is not configured, GitLab couldn't communicate with the user's system, etc. This will better help users to troubleshoot why their graphs aren't working.

Intended users

Further details

Proposal

We need to pass no data reasons to the frontend.

Permissions and Security

Documentation

Testing

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

Links / references