Doc: Update Kolla Ceph document for mixed Ceph OSD deployment

Since Rocky release Kolla Ceph supports both bluestore and
filestore Ceph OSD. In multinode mode, users can overwrite
“ceph_osd_store_type” in the inventory file and deploy the mixed
Ceph OSD.

Change-Id: I4582861c81fdea5fb67114cf3ac1e48f7812f0d7
Signed-off-by: tone.zhang <tone.zhang@arm.com>