feat: PC-12282 Introduce metadata annotations

[skrolikiewicz]

Release Notes

Added the ability to define annotations on SLOs, Services, Projects, and Alert Policies.
Similarly to Kubernetes, users can now use either labels or annotations to attach metadata to objects.

The changes are compatible with the Nobl9 1.75, which will be released on 11.04.2024.

Summary

This PR introduces a mechanism for users to define annotations on SLOs, Services, Projects, and Alert Policies (the same objects to which we can assign labels).
Similarly to Kubernetes, users can use either labels or annotations to attach metadata to objects.

Annotations, similarly to k8s annotations, are defined as key/value maps:

"metadata": {
  "annotations": {
    "key1" : "value1",
    "key2" : "value2"
  }
}

[nieomylnieja]

nicely done :)