Change the default StorageClass name from default-class to default

[ialidzhikov]

How to categorize this PR?

/kind enhancement
/platform vsphere

What this PR does / why we need it:
Similar to gardener/gardener#8565. See the PR description of gardener/gardener#8565 for the motivation of this change.

The StorageClass is mainly used during PVC provisioning. I also tested and verified that a PVC with a deleted StorageClass can be successfully attached/detached, mounted/unmounted and deleted.
However, the PVC resize operation requires the StorageClass to be existing. Trying to send an update request that increases the size of the PVC fails with:

error: persistentvolumeclaims "claim" could not be patched: persistentvolumeclaims "claim" is forbidden: only dynamically provisioned pvc can be resized and the storageclass that provisions the pvc must support resize

However, I think that this should be acceptable because:

• provider-vsphere is not yet productively used
• if needed, the issue can be mitigated by copying the StorageClass with name default and created one with name default-class

---

Currently the default StorageClass of all provider extensions is named default:

• provider-local: https://github.com/gardener/gardener/blob/a47845c1923515fd718fa9386988208227bf83bb/pkg/provider-local/charts/shoot-storageclasses/templates/storageclasses.yaml#L4
• provider-alicloud: https://github.com/gardener/gardener-extension-provider-alicloud/blob/c3958fdf369782fc47eb7fb4d29ab161870c7c2f/charts/internal/shoot-storageclasses/templates/storageclasses.yaml#L5
• provider-aws: https://github.com/gardener/gardener-extension-provider-aws/blob/926f5f8275a5f4c9ef7cab2f2c313f5f120e9957/charts/internal/shoot-storageclasses/templates/storageclasses.yaml#L5
• provider-azure: https://github.com/gardener/gardener-extension-provider-azure/blob/86757db17121163efdd997d392036f1ddcef2e4b/charts/internal/shoot-storageclasses/templates/storageclasses.yaml#L5
• provider-gcp: https://github.com/gardener/gardener-extension-provider-gcp/blob/3713a0c61b59e1baa344c034b45435e2c83bd868/charts/internal/shoot-storageclasses/templates/storageclasses.yaml#L5
• provider-openstack: https://github.com/gardener/gardener-extension-provider-openstack/blob/a5f49663d1d6fb5d9a4e2e9e1b651edb2e346005/pkg/controller/controlplane/valuesprovider.go#L483-L487

Which issue(s) this PR fixes:
Related to gardener/gardener-extension-registry-cache#3

Special notes for your reviewer:
N/A

Release note:

The default StorageClass is renamed from `default-class` to `default`. PVC referring to the `default-class` should continue to successfully attach/detach,  mount/unmount and delete. However, only the resize operation will be affected. If resize is needed for such PVC, then a StorageClass with name `default-class` (copy of the `default` StorageClass) can be temporary created.