ceph: reverting the time delay of 'CephMonHighNumberOfLeaderChanges'

As 'CephMonHighNumberOfLeaderChanges' means there is a
multiple monitor election and indicate some communication
issue between the monitors. Increasing interval timing for
this alert is not considered as safe. So reverting this
change back to 5m

Signed-off-by: Arun Kumar Mohan <amohan@redhat.com>

cluster/examples/kubernetes/ceph/monitoring/prometheus-ceph-v14-rules.yaml

@@ -91,7 +91,7 @@ spec:
         storage_type: ceph
       expr: |
         (ceph_mon_metadata{job="rook-ceph-mgr"} * on (ceph_daemon) group_left() (rate(ceph_mon_num_elections{job="rook-ceph-mgr"}[5m]) * 60)) > 0.95
-      for: 15m
+      for: 5m
       labels:
         severity: warning
   - name: ceph-node-alert.rules