Delete stale metrics on object delete

[darkowlzz]

Depends on fluxcd/pkg#612 .

Move record suspend metrics next to readiness and duration metrics so
that it gets recorded along with others metrics always at the end and the
metrics delete, which requires the knowledge of deleted finalizers,
applies to suspend metrics too.

HelmRepository cache event metrics for a given helmrepo also continues
to be exported even after the object is deleted. This change deletes
the cache event metrics when the object is deleted.

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

# HELP gotk_reconcile_condition The current condition status of a GitOps Toolkit resource reconciliation.
# TYPE gotk_reconcile_condition gauge
gotk_reconcile_condition{kind="GitRepository",name="flux-monitoring",namespace="flux-system",status="False",type="Ready"} 0
gotk_reconcile_condition{kind="GitRepository",name="flux-monitoring",namespace="flux-system",status="True",type="Ready"} 1
gotk_reconcile_condition{kind="GitRepository",name="flux-monitoring",namespace="flux-system",status="Unknown",type="Ready"} 0
gotk_reconcile_condition{kind="HelmChart",name="monitoring-kube-prometheus-stack",namespace="monitoring",status="False",type="Ready"} 0
gotk_reconcile_condition{kind="HelmChart",name="monitoring-kube-prometheus-stack",namespace="monitoring",status="True",type="Ready"} 1
gotk_reconcile_condition{kind="HelmChart",name="monitoring-kube-prometheus-stack",namespace="monitoring",status="Unknown",type="Ready"} 0
...
# HELP gotk_suspend_status The current suspend status of a GitOps Toolkit resource.
# TYPE gotk_suspend_status gauge
gotk_suspend_status{kind="GitRepository",name="flux-monitoring",namespace="flux-system"} 0
gotk_suspend_status{kind="HelmChart",name="monitoring-kube-prometheus-stack",namespace="monitoring"} 0
...
# HELP gotk_cache_events_total Total number of cache retrieval events for a Gitops Toolkit resource reconciliation.
# TYPE gotk_cache_events_total counter
gotk_cache_events_total{event_type="cache_hit",name="podinfo",namespace="default"} 3
gotk_cache_events_total{event_type="cache_miss",name="podinfo",namespace="default"} 1
...

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