Description of problem:
-----------------------

At present, metrics counters for the average/sum of time taken to sync all the snapshots are provided.
 
Metrics should be provided or enable monitoring logic to generate the following alerts:

* Metrics reflecting the alerts for start time of data replication.
* Metrics reflecting the alerts for end time of data replication.
* Metrics reflecting the alerts for time taken for the data replication(single snapshot replication) to complete

Also. include the metrics for start/end when a data replication restarts due to some failures.

Metrics available at present : 
------------------------------


  {
    "key": "cephfs_mirror_peers",
    "value": [
      {
        "labels": {
          "peer_cluster_filesystem": "cephfs",
          "peer_cluster_name": "remote_site",
          "source_filesystem": "cephfs",
          "source_fscid": "1"
        },
        "counters": {
          "snaps_synced": 201,
          "snaps_deleted": 200,
          "snaps_renamed": 0,
          "sync_failures": 1,
          "avg_sync_time": {
            "avgcount": 201,
            "sum": 21.406007450,
            "avgtime": 0.106497549
          },
          "sync_bytes": 132
        }
      }
    ]
  }