[GEP-20] Configure high-availability settings for gardener-resource-manager

[timuthy]

How to categorize this PR?

/area high-availability
/area control-plane
/kind enhancement

What this PR does / why we need it:
This PR adds Pod Topology Spread Constraints to the gardener-resource-manager of shoot control-planes and replaces the formerly used podAntiAffinity.

Which issue(s) this PR fixes:
Fixes parts of #6529

Special notes for your reviewer:
Since the Pod Topology Webook is not applied to GRM itself, we need to workaround the rolling update issue kubernetes/kubernetes#98215 directly in the deployment procedure.

Release note:

The `gardener-resource-manager` deployment was changed from pod anti-affinity to [Topology Spread Constraints](https://kubernetes.io/docs/concepts/scheduling-eviction/topology-spread-constraints/). Non-HA shoot clusters will still have the `gardener-resource-manager` pods being scheduled on different nodes on a best-effort basis. For HA clusters, the Topology Spread Constraints make sure that a distribution across nodes (single-zone) and zones (multi-zonal) is guaranteed, in order to tolerate failures in these domains.

[gardener-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[gardener-prow]

@timuthy: 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-gardener-check-vulnerabilities	570378a	link	false	/test pull-gardener-check-vulnerabilities

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[timuthy]

/test pull-gardener-integration

[rfranzke]

Thanks, sounds reasonable!
/lgtm
/approve

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rfranzke

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[shafeeqes]

/milestone v1.56