Expose an "applied_revision" prometheus metric

[romainmeunier]

We currently have this reconciliation metric :

gotk_reconcile_condition{kind="Kustomization",name="flux-system",namespace="flux-system",status="True",type="Ready"} 1

This metric doesn't expose the revision, which is a crucial information, especially in a multi-tenancy environment.

[seh]

That's likely out of concern for the high cardinality of such a metric label's values.

[kingdonb]

Please refer to:

• Support for flux custom metrics #4128

This has been addressed, now you can create any metrics that you wish if the information is in the CRD spec or status, you can create a metric to report on it.

See also:

https://fluxcd.io/flux/monitoring/custom-metrics/