rabbit_peer_discovery: Set a timeout when waiting for the proxy group leader

... to exit.

[How]
It should never be stuck obviously™. But in case planets are not
aligned, we wait for its exit with a timeout. If it stays around, this
is not the end of the world.

Follow up to #9797.

Submitted by: @lukebakken

Author: dumbbell

deps/rabbit/src/rabbit_peer_discovery.erl

@@ -515,7 +515,12 @@ query_node_props2([], NodesAndProps, ProxyGroupLeader) ->
     NodesAndProps2 = sort_nodes_and_props(NodesAndProps1),
     %% Wait for the proxy group leader to flush its inbox.
     ProxyGroupLeader ! stop_proxy,
-    receive proxy_stopped -> ok end,
+    receive
+        proxy_stopped ->
+            ok
+    after 120_000 ->
+              ok
+    end,
     NodesAndProps2.
 
 -spec get_node_start_time(Node, Unit, ProxyGroupLeader) -> StartTime when