Add Ceph RGW as a supported backend for the internal registry

Story: As an OpenShift administrator I'd like to be able to rely on Red Hat Ceph's RGW component to provide S3 storage to the internal registry so that I have an alternative to Red Hat ODF's Multi-Cloud Gateway (NooBaa) when running on-prem where I don't need MCG's features.

Acceptance criteria:

• IR supports pre-provisioned RGW-provided S3 buckets
• IR accepts RGW credentials