mgr/dashboard: Use a persistent volume to store Loki DB

mgr/dashboard: Use a persistent volume to store Loki DB

Current Behavior: The Loki configuration directs all data to /tmp/loki, which is not mounted as a persistent volume. This results in data being stored in a temporary location that gets cleared upon container restart.
Expected Behavior: Loki data should be stored in /loki, which is backed by the persistent volume mapped to /var/lib/ceph/<fsid>/loki.<id>/data, ensuring data persistence across container restarts.

Fixes: https://tracker.ceph.com/issues/69029
Signed-off-by: Aashish Sharma <aasharma@redhat.com>
(cherry picked from commit 70f8bdba522912fcef7e0ebbb83c611b1e869223)