Allow s3 for virtual garden etcd

[simcod]

Breaking Change

The Gardener backup config now uses `gardener_backup_infrastructure.provider` instead of `metal_control_plane_host_provider` to configure the backup provider type. This should be non-breaking for the deployments we are aware of but it is advised for operators to validate the value before deploying Gardener.

[robertvolkmann]

@Gerrit91 I cannot find any usage of the variable gardener_shooted_seed_backup_infratructure created by:

 - name: Create backup infrastructure config for shooted seed
  set_fact:
    gardener_shooted_seed_backup_infratructure:
      provider: "{{ gardener_backup_infrastructure.provider }}"
      region: "{{ gardener_backup_infrastructure.region }}"
      secretRef:
        name: "{{ gardener_shooted_seed.name }}-backup-secret"
        namespace: garden
  when: gardener_backup_infrastructure_secret

[Gerrit91]

@Gerrit91 I cannot find any usage of the variable gardener_shooted_seed_backup_infratructure created by:

 - name: Create backup infrastructure config for shooted seed
  set_fact:
    gardener_shooted_seed_backup_infratructure:
      provider: "{{ gardener_backup_infrastructure.provider }}"
      region: "{{ gardener_backup_infrastructure.region }}"
      secretRef:
        name: "{{ gardener_shooted_seed.name }}-backup-secret"
        namespace: garden
  when: gardener_backup_infrastructure_secret

Then you can remove it.