Fix MQTT test flake in Khepri mixed version mode

The following test flaked in CI under Khepri in mixed version mode:
```
make -C deps/rabbitmq_mqtt ct-v5 t=cluster_size_3:will_delay_node_restart RABBITMQ_METADATA_STORE=khepri SECONDARY_DIST=rabbitmq_server-4.0.5 FULL=1
```

The first node took exactly 30 seconds for draining:
```
2025-02-10 15:00:09.550824+00:00 [debug] <0.1449.0> MQTT accepting TCP connection <0.1449.0> (127.0.0.1:33376 -> 127.0.0.1:27005)
2025-02-10 15:00:09.550992+00:00 [debug] <0.1449.0> Received a CONNECT, client ID: sub0, username: undefined, clean start: true, protocol version: 5, keepalive: 60, property names: ['Session-Expiry-Interval']
2025-02-10 15:00:09.551134+00:00 [debug] <0.1449.0> MQTT connection 127.0.0.1:33376 -> 127.0.0.1:27005 picked vhost using plugin_configuration_or_default_vhost
2025-02-10 15:00:09.551219+00:00 [debug] <0.1449.0> User 'guest' authenticated successfully by backend rabbit_auth_backend_internal
2025-02-10 15:00:09.551530+00:00 [info] <0.1449.0> Accepted MQTT connection 127.0.0.1:33376 -> 127.0.0.1:27005 for client ID sub0
2025-02-10 15:00:09.551651+00:00 [debug] <0.1449.0> Received a SUBSCRIBE with subscription(s) [{mqtt_subscription,<<"my/topic">>,
2025-02-10 15:00:09.551651+00:00 [debug] <0.1449.0>                                             {mqtt_subscription_opts,0,false,
2025-02-10 15:00:09.551651+00:00 [debug] <0.1449.0>                                              false,0,undefined}}]
2025-02-10 15:00:09.556233+00:00 [debug] <0.896.0> RabbitMQ metadata store: follower leader cast - redirecting to {rabbitmq_metadata,'rmq-ct-mqtt-cluster_size_3-2-27054@localhost'}
2025-02-10 15:00:09.561518+00:00 [debug] <0.1456.0> MQTT accepting TCP connection <0.1456.0> (127.0.0.1:33390 -> 127.0.0.1:27005)
2025-02-10 15:00:09.561634+00:00 [debug] <0.1456.0> Received a CONNECT, client ID: will, username: undefined, clean start: true, protocol version: 5, keepalive: 60, property names: ['Session-Expiry-Interval']
2025-02-10 15:00:09.561715+00:00 [debug] <0.1456.0> MQTT connection 127.0.0.1:33390 -> 127.0.0.1:27005 picked vhost using plugin_configuration_or_default_vhost
2025-02-10 15:00:09.561828+00:00 [debug] <0.1456.0> User 'guest' authenticated successfully by backend rabbit_auth_backend_internal
2025-02-10 15:00:09.562596+00:00 [info] <0.1456.0> Accepted MQTT connection 127.0.0.1:33390 -> 127.0.0.1:27005 for client ID will
2025-02-10 15:00:09.565743+00:00 [warning] <0.1460.0> This node is being put into maintenance (drain) mode
2025-02-10 15:00:09.565833+00:00 [debug] <0.1460.0> Marking the node as undergoing maintenance
2025-02-10 15:00:09.570772+00:00 [info] <0.1460.0> Marked this node as undergoing maintenance
2025-02-10 15:00:09.570904+00:00 [info] <0.1460.0> Asked to suspend 9 client connection listeners. No new client connections will be accepted until these listeners are resumed!
2025-02-10 15:00:09.572268+00:00 [warning] <0.1460.0> Suspended all listeners and will no longer accept client connections
2025-02-10 15:00:09.572317+00:00 [warning] <0.1460.0> Closed 0 local client connections
2025-02-10 15:00:09.572418+00:00 [warning] <0.1449.0> MQTT disconnecting client <<"127.0.0.1:33376 -> 127.0.0.1:27005">> with client ID 'sub0', reason: maintenance
2025-02-10 15:00:09.572414+00:00 [warning] <0.1000.0> Closed 2 local (Web) MQTT client connections
2025-02-10 15:00:09.572499+00:00 [warning] <0.1456.0> MQTT disconnecting client <<"127.0.0.1:33390 -> 127.0.0.1:27005">> with client ID 'will', reason: maintenance
2025-02-10 15:00:09.572866+00:00 [alert] <0.1000.0> Closed 0 local STOMP client connections
2025-02-10 15:00:09.577432+00:00 [debug] <0.1456.0> scheduled delayed Will Message to topic my/topic for MQTT client ID will to be sent in 10000 ms
2025-02-10 15:00:12.991328+00:00 [debug] <0.1469.0> Will reconcile virtual host processes on all cluster members...
2025-02-10 15:00:12.991443+00:00 [debug] <0.1469.0> Will make sure that processes of 1 virtual hosts are running on all reachable cluster nodes
2025-02-10 15:00:12.992497+00:00 [debug] <0.1469.0> Done with virtual host processes reconciliation (run 3)
2025-02-10 15:00:16.511733+00:00 [debug] <0.1476.0> Will reconcile virtual host processes on all cluster members...
2025-02-10 15:00:16.511864+00:00 [debug] <0.1476.0> Will make sure that processes of 1 virtual hosts are running on all reachable cluster nodes
2025-02-10 15:00:16.514293+00:00 [debug] <0.1476.0> Done with virtual host processes reconciliation (run 4)
2025-02-10 15:00:24.897477+00:00 [debug] <0.1479.0> Will reconcile virtual host processes on all cluster members...
2025-02-10 15:00:24.897607+00:00 [debug] <0.1479.0> Will make sure that processes of 1 virtual hosts are running on all reachable cluster nodes
2025-02-10 15:00:24.898483+00:00 [debug] <0.1479.0> Done with virtual host processes reconciliation (run 5)
2025-02-10 15:00:24.898527+00:00 [debug] <0.1479.0> Will reschedule virtual host process reconciliation after 30 seconds
2025-02-10 15:00:32.994347+00:00 [debug] <0.1484.0> Will reconcile virtual host processes on all cluster members...
2025-02-10 15:00:32.994474+00:00 [debug] <0.1484.0> Will make sure that processes of 1 virtual hosts are running on all reachable cluster nodes
2025-02-10 15:00:32.996539+00:00 [debug] <0.1484.0> Done with virtual host processes reconciliation (run 6)
2025-02-10 15:00:32.996585+00:00 [debug] <0.1484.0> Will reschedule virtual host process reconciliation after 30 seconds
2025-02-10 15:00:39.576325+00:00 [info] <0.1460.0> Will transfer leadership of 0 quorum queues with current leader on this node
2025-02-10 15:00:39.576456+00:00 [info] <0.1460.0> Leadership transfer for quorum queues hosted on this node has been initiated
2025-02-10 15:00:39.576948+00:00 [info] <0.1460.0> Will stop local follower replicas of 0 quorum queues on this node
2025-02-10 15:00:39.576990+00:00 [info] <0.1460.0> Stopped all local replicas of quorum queues hosted on this node
2025-02-10 15:00:39.577120+00:00 [info] <0.1460.0> Will transfer leadership of metadata store with current leader on this node
2025-02-10 15:00:39.577282+00:00 [info] <0.1460.0> Khepri clustering: transferring leadership to node 'rmq-ct-mqtt-cluster_size_3-2-27054@localhost'
2025-02-10 15:00:39.577424+00:00 [info] <0.1460.0> Khepri clustering: skipping leadership transfer, leader is already in node 'rmq-ct-mqtt-cluster_size_3-2-27054@localhost'
2025-02-10 15:00:39.577547+00:00 [info] <0.1460.0> Leadership transfer for metadata store on this node has been done. The new leader is 'rmq-ct-mqtt-cluster_size_3-2-27054@localhost'
2025-02-10 15:00:39.577674+00:00 [info] <0.1460.0> Node is ready to be shut down for maintenance or upgrade
2025-02-10 15:00:39.595638+00:00 [notice] <0.64.0> SIGTERM received - shutting down
2025-02-10 15:00:39.595638+00:00 [notice] <0.64.0>
2025-02-10 15:00:39.595758+00:00 [debug] <0.44.0> Running rabbit_prelaunch:shutdown_func() as part of `kernel` shutdown
```

Running the same test locally revealed that [rabbit_maintenance:status_consistent_read/1](https://github.com/rabbitmq/rabbitmq-server/blob/55ae91809433d9e6edfcc98563bcb2f0736ee79e/deps/rabbit/src/rabbit_maintenance.erl#L131)
takes exactly 30 seconds to complete.

The test case assumes a Will Delay higher than the time it takes to
drain and shut down the node. Hence, this commit increases the Will
Delay time from 10 seconds to 40 seconds.

(cherry picked from commit 38cba9d)
(cherry picked from commit fa8669f)

Author: ansd

deps/rabbitmq_mqtt/test/v5_SUITE.erl

@@ -1665,7 +1665,8 @@ will_delay_node_restart(Config) ->
     {ok, _, [0]} = emqtt:subscribe(Sub0a, Topic),
     Sub1 = connect(<<"sub1">>, Config, 1, []),
     {ok, _, [0]} = emqtt:subscribe(Sub1, Topic),
-    WillDelaySecs = 10,
+    %% In mixed version mode with Khepri, draining the node can take 30 seconds.
+    WillDelaySecs = 40,
     C0a = connect(<<"will">>, Config, 0,
                   [{properties, #{'Session-Expiry-Interval' => 900}},
                    {will_props, #{'Will-Delay-Interval' => WillDelaySecs}},