[GEP-20] Change StorageClass to WaitForFirstConsumer

[timuthy]

How to categorize this PR?

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

What this PR does / why we need it:
This PR changes the gardener.cloud-fast storage class do define volumeBindingMode: WaitForFirstConsumer. Scheduling HA shoot control-planes requires the volume creation to respect podAffinity and podAntiaffinities, so that stateful pods can either be schedules across zones or in a single zone only (zone pinning). Without this change, volumes are created in random zones which makes affected pods being stuck in Pending (ref).

Which issue(s) this PR fixes:
Fixes partially gardener/gardener#6529

Special notes for your reviewer:
/cc @kon-angelo

Release note:

The `gardener.cloud-fast` storage class is now deployed with `volumeBindingMode: WaitForFirstConsumer`. This change is required if stateful pods with volumes have a topology related `podAffinity` or `podAntiAffinity` defined, e.g. when Gardener creates control-planes for HA shoot clusters.

[kon-angelo]

/lgtm