Adding a Monitoring Mixin for Skipper

[muaazsaleem]

To help OSS users operate Skipper, adding a monitoring mixin, along with ci checks.

Mixins are a collection of Grafana Dashboards + Prometheus rules & alerts as code. Link: https://monitoring.mixins.dev/

Signed-off-by: Muaaz Saleem [email protected]

[muaazsaleem]

Thanks for the review! Just an update, I'm still committed to addressing the comments as soon as I have an afternoon free 🌤️

[jonathanbeber]

related to #1771