Add a 'raft_cluster' prometheus tag for a Ra cluster name to ra_metrics

Adds a `<<"raft_cluster">>` tag for ra_metrics emitted by QQs, the
stream coordinator, and Khepri.

Before:

    $ curl -s "localhost:15692/metrics/detailed?family=ra_metrics" | grep rabbitmq_detailed_raft_log_last_written_index
    # TYPE rabbitmq_detailed_raft_log_last_written_index gauge
    # HELP rabbitmq_detailed_raft_log_last_written_index Raft log last written index
    rabbitmq_detailed_raft_log_last_written_index 0
    rabbitmq_detailed_raft_log_last_written_index{vhost="/",queue="qq"} 0
    rabbitmq_detailed_raft_log_last_written_index 11

After:

    $ curl -s "localhost:15692/metrics/detailed?family=ra_metrics" | grep rabbitmq_detailed_raft_log_last_written_index
    # TYPE rabbitmq_detailed_raft_log_last_written_index gauge
    # HELP rabbitmq_detailed_raft_log_last_written_index Raft log last written index
    rabbitmq_detailed_raft_log_last_written_index{raft_cluster="rabbitmq_metadata"} 11
    rabbitmq_detailed_raft_log_last_written_index{queue="qq",raft_cluster="%2F_qq",vhost="/"} 51
    rabbitmq_detailed_raft_log_last_written_index{raft_cluster="rabbit_stream_coordinator"} 0

deps/rabbit/src/rabbit_khepri.erl

@@ -260,8 +260,10 @@ setup(_) ->
                       {default_store_id, ?STORE_ID},
                       {default_ra_system, ?RA_SYSTEM}]}],
            [{persistent, true}]),
+    MetricsKey = #{<<"raft_cluster">> => atom_to_binary(?RA_CLUSTER_NAME)},
     RaServerConfig = #{cluster_name => ?RA_CLUSTER_NAME,
-                       friendly_name => ?RA_FRIENDLY_NAME},
+                       friendly_name => ?RA_FRIENDLY_NAME,
+                       metrics_key => MetricsKey},
     case khepri:start(?RA_SYSTEM, RaServerConfig) of
         {ok, ?STORE_ID} ->
             wait_for_leader(),

deps/rabbit/src/rabbit_quorum_queue.erl

@@ -1867,7 +1867,8 @@ make_ra_conf(Q, ServerId, Membership) ->
 
 make_ra_conf(Q, ServerId, TickTimeout,
              SnapshotInterval, CheckpointInterval, Membership) ->
-    QName = amqqueue:get_name(Q),
+    #resource{name = QNameBin, virtual_host = VHostName} = QName =
+      amqqueue:get_name(Q),
     RaMachine = ra_machine(Q),
     [{ClusterName, _} | _] = Members = members(Q),
     UId = ra:new_uid(ra_lib:to_binary(ClusterName)),
@@ -1877,12 +1878,15 @@ make_ra_conf(Q, ServerId, TickTimeout,
                snapshot_interval => SnapshotInterval,
                min_checkpoint_interval => CheckpointInterval,
                max_checkpoints => 3},
+    MetricsKey = #{<<"queue">> => QNameBin,
+                   <<"vhost">> => VHostName,
+                   <<"raft_cluster">> => atom_to_binary(ClusterName, utf8)},
     rabbit_misc:maps_put_truthy(membership, Membership,
                                 #{cluster_name => ClusterName,
                                   id => ServerId,
                                   uid => UId,
                                   friendly_name => FName,
-                                  metrics_key => QName,
+                                  metrics_key => MetricsKey,
                                   initial_members => Members,
                                   log_init_args => LogCfg,
                                   tick_timeout => TickTimeout,

deps/rabbit/src/rabbit_stream_coordinator.erl

@@ -1256,11 +1256,12 @@ make_ra_conf(Node, Nodes) ->
     Members = [{?MODULE, N} || N <- Nodes],
     TickTimeout = application:get_env(rabbit, stream_tick_interval,
                                       ?TICK_TIMEOUT),
+    MetricsKey = #{<<"raft_cluster">> => atom_to_binary(?MODULE)},
     #{cluster_name => ?MODULE,
       id => {?MODULE, Node},
       uid => UId,
       friendly_name => atom_to_list(?MODULE),
-      metrics_key => ?MODULE,
+      metrics_key => MetricsKey,
       initial_members => Members,
       log_init_args => #{uid => UId},
       tick_timeout => TickTimeout,