mon: show count of active/total nvmeof gws in "ceph -s"

mon: show count of active/total nvmeof gws in "ceph -s"

Improve "ceph status" output for nvmeof service:

1. Group by service_id (<pool>.<group>) instead of
  just by gateway groups.
2. Show total gateway count from NVMeofGwMap, and count
  of active gateways.

New output:
```
  services:
    mon:                     4 daemons, quorum ceph-nvme-vm31,ceph-nvme-vm28,ceph-nvme-vm30,ceph-nvme-vm29 (age 16m)
    mgr:                     ceph-nvme-vm31.wnfclf(active, since 18m), standbys: ceph-nvme-vm29.iuwqin, ceph-nvme-vm28.lnnyui, ceph-nvme-vm30.fitwnw
    osd:                     4 osds: 4 up (since 14m), 4 in (since 15m)
    nvmeof (mypool.mygroup1): 2 gateways: 1 active (ceph-nvme-vm30.kkcfux)
    nvmeof (mypool.mygroup2): 2 gateways: 2 active (ceph-nvme-vm28.mfqucr, ceph-nvme-vm29.hrizzl)
```

Signed-off-by: Vallari Agrawal <vallari.agrawal@ibm.com>