Refactor Grafana reconcile loop

[Baarsgaard]

• Feat: Added namespace label to instance metrics, instances sharing names across namespaces are now have separate counters.
• Feat: AllowApplyFailed condition tests to still work by adding a grafana/skip-ready-check annotation to instances.
• Refactor: Grafana status is now updated once in a deferred function and not needlessly copied.
• Refactor: all Grafana instance reconciler signatures no longer take a GrafanaStatus struct
  Locally unused args are prefixed with _ for clarity
• Refactor: Moved r.getVersion from GrafanaReconciler to CompleteReconciler
  External and internal instances now use the same reconciliation logic.
  Failing to fetch the version now marks the instance unready status.stageStatus=failed with a status.lastMessage
  This allows sorting out External instances as unready by GetScopedMatchingInstances.
• Test: new condition option stage=complete stageStatus=failed on instances.

New namespace metric label:

# kubectl port-forward -n grafana-operator-system deployments/grafana-operator-controller-manager-v5 9090 &
# curl http://localhost:9090/metrics | grep namespace=

grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="GET",namespace="default",status="200"} 2362
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="GET",namespace="default",status="404"} 5
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="POST",namespace="default",status="200"} 3
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="POST",namespace="default",status="201"} 2
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="POST",namespace="default",status="202"} 1
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="PUT",namespace="default",status="200"} 786
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="PUT",namespace="default",status="202"} 1052
grafana_operator_grafana_api_requests{instance_name="grafana-testdata",method="PUT",namespace="default",status="500"} 1
grafana_operator_reconciler_failed_reconciles{instance_name="grafana",namespace="default",stage="complete"} 5
grafana_operator_reconciler_failed_reconciles{instance_name="grafana",namespace="default",stage="ingress"} 13
grafana_operator_reconciler_failed_reconciles{instance_name="grafana-testdata",namespace="default",stage="complete"} 12
grafana_operator_reconciler_reconciles{instance_name="grafana",namespace="default"} 18
grafana_operator_reconciler_reconciles{instance_name="grafana-testdata",namespace="default"} 13

[weisdd]

Let's add the comment explaining usage of readiness checks here.
Also, let's rename it from readyCheck to readinessCheck.