refactor(metrics): restructure pkg/metrics and expose GetMetrics for volume Prometheus metrics

[iltyty]

What type of PR is this?

/kind refactor

What this PR does / why we need it:

Restructure pkg/metrics and expose GetMetrics for volume Prometheus metrics.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

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

[k8s-ci-robot]

@iltyty: The label(s) kind/refactor cannot be applied, because the repository doesn't have them.

Details

In response to this:

What type of PR is this?

/kind refactor

What this PR does / why we need it:

Restructure pkg/metrics and expose GetMetrics for volume Prometheus metrics.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

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

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: iltyty
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[k8s-ci-robot]

PR needs rebase.

Details

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[k8s-ci-robot]

@iltyty: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-alibaba-cloud-csi-driver-verify-unit	80331ee	link	true	/test pull-alibaba-cloud-csi-driver-verify-unit
pull-alibaba-cloud-csi-driver-verify-fmt	80331ee	link	true	/test pull-alibaba-cloud-csi-driver-verify-fmt
pull-alibaba-cloud-csi-driver-verify-vet	80331ee	link	true	/test pull-alibaba-cloud-csi-driver-verify-vet
pull-alibaba-cloud-csi-driver-verify-deps	80331ee	link	true	/test pull-alibaba-cloud-csi-driver-verify-deps
pull-alibaba-cloud-csi-driver-verify-lint	80331ee	link	true	/test pull-alibaba-cloud-csi-driver-verify-lint

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Details

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