[openstack-helm] Get rid of cephfs and rbd provisioners

Hi everyone,

I would like to suggest getting rid of cephfs and rbd provisioners. They have been retired and have not been maintained for about 2.5 years now [1]. I believe the CSI approach is what all users rely on nowadays and we can safely remove them.

The trigger for this suggestion is that we are currently experiencing issues while trying to switch cephfs provisioner to Ubuntu Focal and fixing this is just wasting time. [2] Stephen spent some time debugging the issues and can give more details if needed.

What do you think?

[1] https://github.com/kubernetes-retired/external-storage/tree/master/ceph [2] https://review.opendev.org/c/openstack/openstack-helm-infra/+/872976