feat: Expose HRQ limit and usage on metrics endpoint.

[ryotarai]

This exposes HRQ limit and usage on the metrics endpoint.

The metric labels align with kube_resourcequota metric of kube-state-metrics.

$ curl --silent localhost:8080/metrics | grep hnc_hierarchicalresourcequota
# HELP hnc_hierarchicalresourcequota HRQ hard/used like kube_resourcequota
# TYPE hnc_hierarchicalresourcequota gauge
hnc_hierarchicalresourcequota{hrq="test-a",namespace="test-parent",resource="cpu",type="hard"} 20
hnc_hierarchicalresourcequota{hrq="test-a",namespace="test-parent",resource="cpu",type="used"} 0
hnc_hierarchicalresourcequota{hrq="test-a",namespace="test-parent",resource="memory",type="hard"} 4.294967296e+10
hnc_hierarchicalresourcequota{hrq="test-a",namespace="test-parent",resource="memory",type="used"} 0

[superbrothers]

• Please document metrics in HRQ's documentation.
• Please verify that the hnc_ prefix for metric names aligns with the existing metric prefix.

[ryotarai]

$ curl --silent localhost:8080/metrics | grep -v ^# | cut -d'_' -f1 | sort | uniq 
certwatcher
controller
go
hnc
process
rest
workqueue

$ curl --silent localhost:8080/metrics | grep ^hnc_   
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="AncestorHaltActivities"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="DeletingCRD"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="IllegalManagedAnnotation"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="IllegalManagedLabel"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="IllegalParent"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="InCycle"} 0
hnc_namespace_conditions{Condition="ActivitiesHalted",Reason="ParentMissing"} 0
hnc_namespace_conditions{Condition="BadConfiguration",Reason="SubnamespaceAnchorMissing"} 0
hnc_reconcilers_hierconfig_concurrent_peak 0
hnc_reconcilers_hierconfig_namespace_writes_total 62
hnc_reconcilers_hierconfig_total 22
hnc_reconcilers_object_concurrent_peak{GroupKind=""} 0
hnc_reconcilers_object_total{GroupKind=""} 8

[superbrothers]

@utam0k Could you please take a look at this PR?

[utam0k]

Thanks!