feat: add metrics to show target size of every node group

[guopeng0]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR aims to add a new metric that displays the target size of all node groups.This metric is essential for obtaining a clear understanding of the target size of each node group while using the cluster autoscaler.

for example, we can on comparing this metric with the number of Kubernetes nodes to determine if the environment behaves as expected.This is crucial in detecting issues promptly, especially in the production environment.

The periodic update of this value has already been implemented in the UpdateNodes function of ClusterStateRegistry.We just need to add the reporting metrics functionality.This method does not increase the number of calls to the cloud provider nor does it affect other logic.

We kindly request your review of this PR and your thoughts on the proposed implementation.

Thank you for your time and consideration.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[x13n]

/assign

[x13n]

Thanks for the change! It would be a bit more consistent with other metrics if it was exported with them:

autoscaler/cluster-autoscaler/core/static_autoscaler.go

Lines 339 to 345 in b4586f9

	// Update node groups min/max and maximum number of nodes being set for all node groups after cloud provider refresh
	maxNodesCount := 0
	for _, nodeGroup := range a.AutoscalingContext.CloudProvider.NodeGroups() {
	metrics.UpdateNodeGroupMin(nodeGroup.Id(), nodeGroup.MinSize())
	metrics.UpdateNodeGroupMax(nodeGroup.Id(), nodeGroup.MaxSize())
	maxNodesCount += nodeGroup.MaxSize()
	}

Though I guess it could have performance implications for cloud provideres that don't cache target size, so let's merge as is.

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guopeng0, x13n

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[guopeng0]

@x13n Thank you so much for merging my Pull Request