MB-49448 Add server group to "nodes" section of REST response

This change adds the serverGroup name for each node in the "nodes"
section of REST responses that include it.

  "nodes": [
    {
      "clusterMembership": "active",
      "recoveryType": "none",
      "status": "healthy",
      "otpNode": "n_0@127.0.0.1",
      "thisNode": true,
      "hostname": "[::1]:9000",
      "nodeUUID": "58c43cea27e1a899b292056c0b4c6040",
      "serverGroup": "group1",                  <<<<<<<<<<<<<<<<

For REST endpoints such as....

/pools/default
/poolsStreaming/default
/pools/default/buckets
/pools/default/buckets/<bucketName>
/pools/nodes

Change-Id: I98c26d0c5cfd3bbff57d700e8d2ff0ad2e4e8487
Reviewed-on: https://review.couchbase.org/c/ns_server/+/165564
Well-Formed: Build Bot <build@couchbase.com>
Tested-by: Steve Watanabe <steve.watanabe@couchbase.com>
Reviewed-by: Abhijeeth Nuthan <abhijeeth.nuthan@couchbase.com>

src/menelaus_web_node.erl

@@ -530,9 +530,12 @@ build_node_info(Config, Snapshot, WantENode, InfoNode, LocalAddr) ->
                     L ->
                         [{[{afamily, AF}, {nodeEncryption, E}]} || {AF, E} <- L]
                 end,
+    ServerGroup = ns_cluster_membership:get_node_server_group(WantENode,
+                                                              Config),
 
     RV = [{hostname, build_node_hostname(Config, WantENode, LocalAddr)},
           {nodeUUID, NodeUUID},
+          {serverGroup, ServerGroup},
           {clusterCompatibility,
            cluster_compat_mode:effective_cluster_compat_version()},
           {version, list_to_binary(Version)},