Drop support for Shoots with Kubernetes version == 1.24

[shafeeqes]

How to categorize this PR?

/kind cleanup

What this PR does / why we need it:
Drop support for Shoots, Seeds and Gardens with Kubernetes version == 1.24.

Notable changes:

• Drop deploying PSP resources and handling for PSP migration
• Deprecate allowPrivilegedContainers field in the Shoot API.
• Adapt Seccomp profile defaulting: https://github.com/gardener/gardener/blob/master/docs/usage/default_seccomp_profile.md
• Drop kubeapiserver watchdog sidecar, https://github.com/gardener/gardener/blob/5b76b2ed9066f69b8b71d9c150914d812a65879c/pkg/component/kubeapiserver/deployment.go#L400C1-L406C4
• Drop workaround for kubeproxy:

  gardener/pkg/component/kubeproxy/resources/cleanup.sh

  Lines 9 to 16 in 5b76b2e

  	# Workaround kube-proxy bug (https://github.com/kubernetes/kubernetes/issues/109286) when switching from ipvs to iptables mode.
  	# The fix (https://github.com/kubernetes/kubernetes/pull/109288) is present in 1.25+.
  	if [ "${EXECUTE_WORKAROUND_FOR_K8S_ISSUE_109286}" = "true" ]; then
  	if iptables -t filter -L KUBE-NODE-PORT; then
  	echo "KUBE-NODE-PORT chain exists, flushing it..."
  	iptables -t filter -F KUBE-NODE-PORT
  	fi
  	fi

Which issue(s) this PR fixes:
Part of #8921

Special notes for your reviewer:
Please follow the dedicated commits for easy reviewing.

Release note:

⚠️ Gardener does no longer support garden, seed, or shoot clusters with Kubernetes versions == 1.24. Make sure to upgrade all existing clusters before upgrading to this Gardener version.

The `spec.kubernetes.allowPrivilegedContainers` field in the Shoot API is deprecated and will be removed in a future version. This field is not relevant to Shoots with kubernetes versions >= 1.25. Please adapt your controllers accordingly.

[acumino]

/assign

[oliver-goetz]

/assign

[shafeeqes]

/hold until gardener v1.89 is released due to a change in plans of the expiry of v1.24.

[shafeeqes]

Force-pushed to resolve the conflicts.

[rfranzke]

/lgtm

[gardener-prow]

LGTM label has been added.

Git tree hash: 9bdf91019c809065c31ec6ccbe0e6c42693a3f7d