Revendor gardener/gardener@v1.48.0-dev (bd4e6e20cacb) and support for Kubernetes 1.24

[rfranzke]

How to categorize this PR?

/area open-source
/kind enhancement

What this PR does / why we need it:
This PR revendors gardener/gardener@v1.48.0-dev (gardener/gardener@bd4e6e2) to allow starting an early release validation cycle.
Also, with this it adds support for Kubernetes 1.24 to the extension.

Which issue(s) this PR fixes:
Part of gardener/gardener#3292
Part of gardener/gardener#5912

Special notes for your reviewer:
We have to revendor gardener/gardener@v1.48.0 once it's released before releasing this extension.

Special notes for your reviewer:

• I have not validated the functionality as follows due to missing test/dev environment:
  • ❔ Create new clusters with versions < 1.24
  • ❔ Create new clusters with version = 1.24
  • ❔ Upgrade old clusters from version 1.23 to version 1.24
  • ❔ Delete clusters with versions < 1.24
  • ❔ Delete clusters with version = 1.24

Release note:

The extension does now automatically rotate its webhook CA and server certificates each `30d`.

This extension is prepared to support the Shoot `ServiceAccount` signing key rotation feature ([see documentation](https://github.com/gardener/gardener/blob/master/docs/usage/shoot_credentials_rotation.md#serviceaccount-token-signing-key)).

The Equinix Metal extension does now support shoot clusters with Kubernetes version 1.23. You should consider the [Kubernetes release notes](https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.23.md) before upgrading to 1.23.