rabbit: Stop Khepri store and Ra systems in stop/1

[Why]
The Khepri store and the coordinators are Ra servers and thus run under
the Ra supervision tree. Therefore we need to explicitly stop them
otherwise they will continue to run after `rabbit` was stopped.

Likewise, the Ra systems are under the Ra supervision tree. We also need
to stop them.

[How]
We need to stop Ra servers and Ra systems that we started but live under
the Ra supervision tree. The order is important:
1. The `quorum_queues` Ra system because it may host Ra servers that
   depend on Khepri.
2. The stream coordinator because it depends on Khepri.
3. The Khepri store; it could be stopped automatically with the
   termination of the underlying Ra system, but Khepri needs to do some
   cleanup too.
4. The remaining Ra systems.

deps/rabbit/src/rabbit.erl

@@ -1079,6 +1079,21 @@ stop(State) ->
         [] -> rabbit_prelaunch:set_stop_reason(normal);
         _  -> rabbit_prelaunch:set_stop_reason(State)
     end,
+
+    %% We need to stop Ra servers and Ra systems that we started but live
+    %% under the Ra supervision tree. The order is important:
+    %% 1. The `quorum_queues` Ra system because it may host Ra servers that
+    %%    depend on Khepri.
+    %% 2. The stream coordinator because it depends on Khepri.
+    %% 3. The Khepri store; it could be stopped automatically with the
+    %%    termination of the underlying Ra system, but Khepri needs to do some
+    %%    cleanup too.
+    %% 4. The remaining Ra systems.
+    rabbit_ra_systems:ensure_ra_system_stopped(quorum_queues),
+    _ = rabbit_stream_coordinator:stop(),
+    rabbit_khepri:stop(),
+    rabbit_ra_systems:ensure_stopped(),
+
     rabbit_db:clear_init_finished(),
     rabbit_boot_state:set(stopped),
     ok.

deps/rabbit/src/rabbit_khepri.erl

@@ -96,6 +96,7 @@
 
 -export([setup/0,
          setup/1,
+         stop/0,
          can_join_cluster/1,
          add_member/2,
          remove_member/1,
@@ -287,6 +288,9 @@ wait_for_leader(Timeout, Retries) ->
             throw(Reason)
     end.
 
+stop() ->
+    ok = khepri:stop(?RA_CLUSTER_NAME).
+
 %% @private
 
 can_join_cluster(DiscoveryNode) when is_atom(DiscoveryNode) ->

deps/rabbit/src/rabbit_ra_systems.erl

@@ -17,6 +17,7 @@
          are_running/0,
          ensure_ra_system_started/1,
          ensure_started/0,
+         ensure_ra_system_stopped/1,
          ensure_stopped/0]).
 
 -type ra_system_name() :: atom().