List connections via tracking on GET /connections

when the metrics collector is disabled.

References  #15975.

Author: michaelklishin

deps/rabbitmq_management/src/rabbit_mgmt_wm_connections.erl

@@ -48,6 +48,15 @@ do_connections_query(ReqData, Context) ->
         false ->
             augmented(ReqData, Context);
         true ->
-            rabbit_mgmt_util:filter_conn_ch_list(
-              rabbit_mgmt_db:get_all_connections(), ReqData, Context)
+            case rabbit_mgmt_agent_config:is_metrics_collector_enabled() of
+                true ->
+                    rabbit_mgmt_util:filter_conn_ch_list(
+                      rabbit_mgmt_db:get_all_connections(), ReqData, Context);
+                false ->
+                    %% IMPORTANT: connection_created_stats is empty when the
+                    %% metrics collector is disabled. Fall back to the
+                    %% tracked-connection list.
+                    rabbit_mgmt_util:filter_tracked_conn_list(
+                      rabbit_connection_tracking:list(), ReqData, Context)
+            end
     end.