Feature: Prometheus Metric service widget

[fcornelius]

Proposed change

Adds a service widget to query prometheus metrics with PromQL queries and formats the results in a very similar way to how customapi does. I tried to combine this with the existing prometheus service widget but since the configuration for this one is quite fundamentally different I thought it makes more sense to have it in a separate widget. Let me know what you think.

Closes #779, #2969, #4267

Type of change

• New service widget
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation only
• Other (please explain)

Checklist:

• If applicable, I have added corresponding documentation changes.
• If applicable, I have reviewed the feature and / or service widget guidelines.
• I have checked that all code style checks pass using pre-commit hooks and linting checks.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.

[shamoon]

Thanks, looks pretty good but some small notes.

There may be some edge cases but generally seems to work great

[fcornelius]

Hey, sorry didn't get a chance to your review your comments until now. Thanks for merging!