Delete stale metrics on object delete

[darkowlzz]

Depends on fluxcd/pkg#612

The metrics helper now accepts owned finalizers to determine if an object is no longer managed by the controller and is being deleted, and deletes the metrics associated with the object.

Before this change, the following metrics continued to be exported even after the associated object is deleted:

gotk_reconcile_condition{kind="Kustomization",name="podinfo",namespace="default",status="False",type="Ready"} 0
gotk_reconcile_condition{kind="Kustomization",name="podinfo",namespace="default",status="True",type="Ready"} 1
gotk_reconcile_condition{kind="Kustomization",name="podinfo",namespace="default",status="Unknown",type="Ready"} 0
...
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="0.01"} 1
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="0.038363583488692544"} 1
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="0.1471764538093883"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="0.5646216173286169"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="2.166090855590701"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="8.309900738254731"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="31.879757075478317"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="122.30217221643493"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="469.19495946736544"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="1799.9999999999986"} 2
gotk_reconcile_duration_seconds_bucket{kind="Kustomization",name="podinfo",namespace="default",le="+Inf"} 2
gotk_reconcile_duration_seconds_sum{kind="Kustomization",name="podinfo",namespace="default"} 0.092792429
gotk_reconcile_duration_seconds_count{kind="Kustomization",name="podinfo",namespace="default"} 2
...
gotk_suspend_status{kind="Kustomization",name="podinfo",namespace="default"} 0

With this change, they get deleted once the associated object is deleted.

Also, the metrics helper no longer exports ConditionDelete for readiness metrics.