mgr: store names of modules that register RADOS clients in the MgrMap

mgr: store names of modules that register RADOS clients in the MgrMap

The MgrMap stores a list of RADOS clients' addresses registered by the
mgr modules. During failover of ceph-mgr, the list is used to blocklist
clients belonging to the failed ceph-mgr.

Store the names of the mgr modules that registered the RADOS clients
along with the clients' addresses in the MgrMap. During debugging, this
allows easy identification of the mgr module that registered a
particular RADOS client by just dumping the MgrMap (`ceph mgr dump`).

Following is the MgrMap output with a module's client name displayed
along with its client addrvec,
$ ceph mgr dump | jq '.active_clients[0]'
{
  "name": "devicehealth",
  "addrvec": [
    {
      "type": "v2",
      "addr": "10.0.0.148:0",
      "nonce": 612376578
    }
  ]
}

Fixes: https://tracker.ceph.com/issues/58691
Signed-off-by: Ramana Raja <rraja@redhat.com>