Drop support for Shoots with Kubernetes version <= 1.26

[RadaBDimitrova]

How to categorize this PR?

/kind cleanup /platform gcp

What this PR does / why we need it:

• [x] Drop support for Shoots, Seeds and Gardens with Kubernetes version <= 1.24.
• [x] Adapt PDBs to use unhealthyPodEvictionPolicy: AlwaysAllow unconditionally
• [x] Adapt service.kubernetes.io/topology-mode annotation
• [x] Adapt controlplane webhook

Which issue(s) this PR fixes: Part of https://github.com/gardener/gardener/issues/10339

Special notes for your reviewer:

In draft until the gardener/gardener PR is merged and released.

Release note:

`provider-gcp` no longer supports Shoots with Кubernetes version <= 1.26.

[aabond]

Hi @RadaBDimitrova ,

We still require support for kubernetes version 1.26. We have a product that is working to become compatible with version 1.27, but it's still a work in progress.

[RadaBDimitrova]

/retest

[kon-angelo]

/hold