tools/cephfs_mirror: Add inprogress bytes and files metric

tools/cephfs_mirror: Add inprogress bytes and files metric

Add following mirroring progress metrics to current_syncing_snap
as below

bytes:
  sync_bytes - bytes synced till now
  total_bytes - total bytes to be synced
  sync_percent - Percentage of bytes synced till now
files:
  total_files - Total files to be synced
  sync_files - files synced till now
  sync_percent - Percentage of files synced till now

sync_files and sync_bytes are also stored in last_synced_snap section
after the snapshot is synced.

The bytes is formatted as below.

Sample output:
--------
{
    "/d0": {
        "state": "syncing",
        "current_syncing_snap": {
            "id": 3,
            "name": "d0_snap1",
            "bytes": {
                "sync_bytes": "120.20 MiB",
                "total_bytes": "149.94 MiB",
                "sync_percent": "80.16%"
            },
            "files": {
                "sync_files": 4032,
                "total_files": 5000,
                "sync_percent": "80.64%"
            }
        },
        "last_synced_snap": {
            "id": 2,
            "name": "d0_snap0",
            "sync_duration": 45,
            "sync_time_stamp": "5642.805770s",
            "sync_bytes": "300.85 MiB",
            "sync_files": 10000
        },
        "snaps_synced": 1,
        "snaps_deleted": 0,
        "snaps_renamed": 0
    }
}

Fixes: https://tracker.ceph.com/issues/73453
Signed-off-by: Kotresh HR <khiremat@redhat.com>