[stable/nginx-ingress] fix service selector(metrics/webhook)

[skomma]

What this PR does / why we need it:

I fixed controller/default-backend service selector in #21512.
But I forgot to fix metrics/webhook service selector.
This PR fixes it.

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [stable/mychartname])

[k8s-ci-robot]

Hi @skomma. Thanks for your PR.

I'm waiting for a helm 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.

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[skomma]

/assign @ChiefAlexander

[taharah]

/lgtm
/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: skomma, taharah

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