vfs_ceph_new: add keybridge and ceph fscrypt support

vfs_ceph_new: add keybridge and ceph fscrypt support

Add support for CephFS's new fscrypt feature. Fetch the key material
using the new keybridge varlink local RPC API.

Adds the following configuration parameters for the vfs_ceph_new module:
```
ceph_new:keybridge socket = unix:/run/keybridge.sock
ceph_new:keybridge scope = mem
ceph_new:keybridge name = test
ceph_new:keybridge kind = B64
ceph_new:fscrypt = keybridge
```

Where the various keybridge parameters configure what keybridge server
to use and what key to fetch. The `ceph_new:fscrypt` parameter defaults to
'disabled' and can be set to 'keybridge'. An enum is used here in case
we ever need to support something other than keybridge in the future.

Pair-Programmed-With: Shachar Sharon <ssharon@redhat.com>
Signed-off-by: Shachar Sharon <ssharon@redhat.com>
Signed-off-by: John Mulligan <jmulligan@redhat.com>
Reviewed-by: Gunther Deschner <gd@samba.org>
Reviewed-by: Anoop C S <anoopcs@samba.org>