Remove direct reference to prometheus.Label

[RainbowMango]

What type of PR is this?
/kind feature

What this PR does / why we need it:
Remove direct reference to Prometheus.Label.

To get metrics stability into Beta, we will make it illegal to directly import prometheus methods in Kubernetes components.

Which issue(s) this PR fixes:
Refer kubernetes/enhancements#1238

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.:

/priority important-soon
/assign @dims @mikedanese
/cc @logicalhan

[dims]

/assign @frapposelli
/lgtm

[frapposelli]

thanks!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: frapposelli, RainbowMango

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• staging/src/k8s.io/legacy-cloud-providers/vsphere/OWNERS [frapposelli]

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[frapposelli]

/test pull-kubernetes-bazel-test

[logicalhan]

/lgtm