Enforce TLS v1.2 or higher for webhook server

[sharath-srikanth-chellappa]

What this PR does / why we need it:

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #329

This patch introduces TLS configuration enforcement for the webhook server in main.go.
Specifically, it ensures that the server uses TLS 1.2 or higher.

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Release notes:

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sharath-srikanth-chellappa
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[nunnatsa]

Thanks for your PR @sharath-srikanth-chellappa !!

I copied it into #328 and it was just got merged.

[k8s-ci-robot]

PR needs rebase.

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