mgr/dashboard: support Orchestrator and user-defined Ganesha clusters

mgr/dashboard: support Orchestrator and user-defined Ganesha clusters

This change make the Dashboard support two types of Ganesha clusters:

- Orchestrator clusters (Since Octopus)
  - Deployed by the Orchestrator.
  - The Dashboard gets the pool/namespace that stores Ganesha
    configuration objects from the Orchestrator.
  - The Dashboard gets the daemons in a cluster from the Orchestrator.

- User-defined clusters (Since Nautilus)
  - Clusters defined by using `ceph dashboard
    set-ganesha-clusters-rados-pool-namespace` command is treated as
    user-defined clusters.
  - Each daemon has its own RADOS configuration objects. The
    Dashboard uses these objects to deduce daemons.

Fixes: https://tracker.ceph.com/issues/46492
Signed-off-by: Kiefer Chang <kiefer.chang@suse.com>