Ensure all user/workspace PVCs have a required PVC type label

[mkuznyetsov]

Description

The #920 issue introduces new labels, that are used for identifying PVCs. This allows for more precise reconciling triggerd by PVC deletion, especially in the case when PVC name was defined in an external devworkspace config.

This however, doesn't affect devworkspaces, that were already existing on the cluster, so for these workpsaces the operator will behave the same way as before issue #920 was resolved. So we must ensure that there is some kind of migration or other process that ensures that required label is present in the actual PVC resource, when new operator will be running

Additional context