mgr/dashboard: upgrade from old 'graph' type panels to the new

mgr/dashboard: upgrade from old 'graph' type panels to the new
'timeseries' panel

The graph panel type is deprecated, and disappears after Grafana v9.1 (current version is 10.0) to prevent more old type panels being created. These should be migrated to the timeseries panel type, to avoid potential problems with future Grafana versions.

Fixes: https://tracker.ceph.com/issues/61720
Signed-off-by: Aashish Sharma <aasharma@redhat.com>