Fix gRPC initialized even without aux type registered (#18928)

* Fix gRPC initialized even without aux type registered.

Signed-off-by: Finn Carroll <carrofin@amazon.com>

* Spotless apply

Signed-off-by: Finn Carroll <carrofin@amazon.com>

---------

Signed-off-by: Finn Carroll <carrofin@amazon.com>

Author: finnegancarroll

modules/transport-grpc/src/main/java/org/opensearch/transport/grpc/GrpcPlugin.java

@@ -45,6 +45,7 @@
 
 import io.grpc.BindableService;
 
+import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.GRPC_TRANSPORT_SETTING_KEY;
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_BIND_HOST;
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_HOST;
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_KEEPALIVE_TIMEOUT;
@@ -55,6 +56,7 @@
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_PUBLISH_HOST;
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_PUBLISH_PORT;
 import static org.opensearch.transport.grpc.Netty4GrpcServerTransport.SETTING_GRPC_WORKER_COUNT;
+import static org.opensearch.transport.grpc.ssl.SecureNetty4GrpcServerTransport.GRPC_SECURE_TRANSPORT_SETTING_KEY;
 import static org.opensearch.transport.grpc.ssl.SecureNetty4GrpcServerTransport.SETTING_GRPC_SECURE_PORT;
 
 /**
@@ -143,8 +145,10 @@ public Map<String, Supplier<AuxTransport>> getAuxTransports(
             new DocumentServiceImpl(client),
             new SearchServiceImpl(client, queryUtils)
         );
-        AuxTransport transport = new Netty4GrpcServerTransport(settings, grpcServices, networkService);
-        return Collections.singletonMap(transport.settingKey(), () -> transport);
+        return Collections.singletonMap(
+            GRPC_TRANSPORT_SETTING_KEY,
+            () -> new Netty4GrpcServerTransport(settings, grpcServices, networkService)
+        );
     }
 
     /**
@@ -184,13 +188,10 @@ public Map<String, Supplier<AuxTransport>> getSecureAuxTransports(
             new DocumentServiceImpl(client),
             new SearchServiceImpl(client, queryUtils)
         );
-        AuxTransport transport = new SecureNetty4GrpcServerTransport(
-            settings,
-            grpcServices,
-            networkService,
-            secureAuxTransportSettingsProvider
+        return Collections.singletonMap(
+            GRPC_SECURE_TRANSPORT_SETTING_KEY,
+            () -> new SecureNetty4GrpcServerTransport(settings, grpcServices, networkService, secureAuxTransportSettingsProvider)
         );
-        return Collections.singletonMap(transport.settingKey(), () -> transport);
     }
 
     /**