Set up a metrics server with data served on /metrics

[laozc]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Expose gRPC prometheus metrics to capture performance for volume operations

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Added flag metrics-bind-addr to specify the endpoint for gRPC server metrics

[k8s-ci-robot]

Hi @laozc. Thanks for your PR.

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[mauriciopoppe]

Thanks for the PR, I left a few comments.

[mauriciopoppe]

I left some comments.

/ok-to-test

[mauriciopoppe]

I wrote a few comments in the setup of the server and on inlining the code. The approach looks good to me, thanks.

[mauriciopoppe]

Thanks a lot for the implementation! I thought we could port the implementation to the library-development branch but I think it's not applicable because the gRPC metrics would already be exposed as part of the CSI Driver metrics (once the CSI Driver uses the library implementation).

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: laozc, mauriciopoppe

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