docs: add controller metrics reference

[OneUpWallStreet]

Description

Added user-facing docs covering all the metrics defined in internal/metrics/metrics.go. I tried to keep the structure simple and extensible so we can build on it as we add more metrics, while still keeping it consistent with the rest of the docs.

I also kept the per-metric detail fairly lightweight for now, so lmk if you want more detail for each metric or if the current level is okay.

Related Issue

Fixes #94

Type of Change

/kind documentation

Testing

N/A

Checklist

• make test passes
• make lint passes

Does this PR introduce a user-facing change?

NONE

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[k8s-ci-robot]

Hi @OneUpWallStreet. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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[ajaysundark]

/lgtm
/approve

thanks

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ajaysundark, OneUpWallStreet

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