feat: #2501 Count volumes attached to a node

[LiuQhahah]

What this PR does / why we need it:

Count volumes attached to a node

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

increaser two metrics: kube_node_volumes_attached_count and kube_node_volumes_in_use_count

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2501

[mrueg]

I understand what you're trying to achieve here, I wonder though if it would be easier to attach a node label to the kube_volumeattachment_status_attached metric or a similar one and then do a sum by that label in promql instead of exposing counts here.

[LiuQhahah]

I understand what you're trying to achieve here, I wonder though if it would be easier to attach a node label to the kube_volumeattachment_status_attached metric or a similar one and then do a sum by that label in promql instead of exposing counts here.

Thanks for the suggestion, from my understanding @thommeo wants to get the number of volumns currently attached from the perspective of node, and kube_volumeattachment_status_attached is from volumnattachment from volumeattachments to count the number of volumns he is attached to by that node attchment.

From my personal understanding and implementation point of view, I think creating a metric will be better understood, the current implementation is not so complex, so that the use of the customer will be more convenient!

[dgrisonnet]

/triage accepted
/assign

[k8s-ci-robot]

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