Make default PVC size configurable

[amisevsk]

Description

PVCs created by the operator by default request 1Gi of storage. The devfile API spec includes a "size" field in volume components, but it would be helpful to be able to configure the default request for creating PVCs as well.

This task is complicated by:

• It's not clear what the size field in a volume component means when a common storage type is used (e.g. all volumes for all workspaces mount the same PVC
• It's unclear how to manage PVC size in general, since most PVCs cannot be dynamically resized.

Additional context

[benoitf]

even trying a custom 'projects' component with a size field didn't worked in my devfile. It was still a 1Gi PV ( from common)