✨ Gracefully shutdown the c/r webhooks

[inteon]

See problem described in #2601.
This PR implements the solution proposed in #2601 (comment).

An interesting article about this topic: https://medium.com/hackernoon/graceful-shutdown-in-kubernetes-435b98794461

[k8s-ci-robot]

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[inteon]

/retest

[k8s-ci-robot]

@inteon: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-controller-runtime-test	f767494	link	true	/test pull-controller-runtime-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[inteon]

replaced by #2601