Allow labelFromKey field for all applicable types

[rexagod]

Allow labelFromKey field for the following types:

• Gauge: Done.
• Info: Done.
• StateSet: N/A (redundant use case, see doc changes for more info).

Fixes: #1871 and #1868.

How does this change affect the cardinality of KSM: Increases (we are adding labels from keys, which may increase cardinality).

[rexagod]

Input

kind: CustomResourceStateMetrics
spec:
  resources:
    - groupVersionKind:
        group: "apps"
        version: "v1"
        kind: "Deployment"
      labelsFromPath:
        name: [metadata, name]
      metrics:
        - name: "test_metrics"
          help: "metrics for debugging"
          each:
            type: Info
            info:
              path: [metadata, annotations]
              labelFromKey: test

Output

# HELP kube_crd_test_metrics metrics for debugging
# TYPE kube_crd_test_metrics gauge (<-- this is a bug, I've added a TODO for this)
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="deployment.kubernetes.io/revision",version="v1"} 1
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="test-a",version="v1"} 1
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="test-b",version="v1"} 2
# HELP kube_crd_test_metrics metrics for debugging
# TYPE kube_crd_test_metrics gauge (<-- this is a bug, I've added a TODO for this)
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="deployment.kubernetes.io/revision",version="v1"} 1
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="test-a",version="v1"} 1
kube_crd_test_metrics{group="apps",kind="Deployment",name="nginx-deployment",test="test-b",version="v1"} 2

[rexagod]

Ready for review.

[CatherineF-dev]

Wondering if it's possible to have an E2E test for CRD metrics.

[mrueg]

/lgtm
/hold
for @dgrisonnet @fpetkovski @logicalhan to have another look

[logicalhan]

/lgtm

[mrueg]

/lgtm

/hold cancel

Thanks for your contribution @rexagod !

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: logicalhan, mrueg, rexagod

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