feature(ci): generate flags & metrics documentation

[vflaux]

What does it do ?

Add jobs check that flags & metrics documentation is up to date.

Motivation

Documentation updates are not validated by CI and changes can be missed in reviews.
See #5834

More

• Yes, this PR title follows Conventional Commits
• Yes, I added unit tests
• Yes, I updated end user documentation accordingly

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @vflaux. 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. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[ivankatliarchuk]

There are unit tests and they executed as part of a build. Worth double check the code