Add raft query parameter to /jsz to include raft group info

[wallyqs]

This adds a new raft query parameter to be able to map a stream/consumer name with its active raft group:

/jsz?consumers=1&raft=1

 "stream_raft_group": "S-R3F-8Qml10Ei",
"consumer_raft_groups": [
  {
    "name": "1",
    "raft_group": "C-R3F-5c87s2aq"
  },
  {
    "name": "10",
    "raft_group": "C-R3F-PF8WWIue"
  },
  {
    "name": "100",
    "raft_group": "C-R3F-r58xhrRe"
  },
  {
    "name": "12",
    "raft_group": "C-R3F-faSs9EY1"
  },

[derekcollison]

Very cool, ping me when ready for review!

[neilalexander]

LGTM!

[derekcollison]

LGTM!

@ripienaar we can add this into CLI.