[8.x] Downgrade transport.enable_stack_protection deprecation to a warning (#124788)

This setting is not getting removed in ES 9.0, so its usage should not generate a critical deprecation warning.

`TransportServiceLifecycleTests` already uses `assertWarnings` instead of `assertCriticalWarnings` and we
don't distinguish between warning levels in assertions (See #80304)

See #109236
See ES-11224

Author: arteam

server/src/main/java/org/elasticsearch/transport/TransportService.java

@@ -101,7 +101,7 @@ public class TransportService extends AbstractLifecycleComponent
         "transport.enable_stack_protection",
         false,
         Setting.Property.NodeScope,
-        Setting.Property.Deprecated
+        Setting.Property.DeprecatedWarning
     );
 
     private final AtomicBoolean handleIncomingRequests = new AtomicBoolean();