fix: update ExchangeSerDe interface to help Spring initialization

It seems the @qualifier was not enough. Since the introduction of
Integration Controller in APIM, we can see the following error

`No qualifying bean of type 'io.gravitee.exchange.api.websocket.command.ExchangeSerDe' available: expected single matching bean but found 2: cockpitExchangeSerDe,integrationExchangeSerDe`

Using the actual implementation resolves the issue.

gravitee-cockpit-connectors-ws/src/main/java/io/gravitee/cockpit/connectors/ws/WebSocketCockpitConnector.java

@@ -16,6 +16,7 @@
 package io.gravitee.cockpit.connectors.ws;
 
 import io.gravitee.cockpit.api.CockpitConnector;
+import io.gravitee.cockpit.api.command.websocket.CockpitExchangeSerDe;
 import io.gravitee.cockpit.connectors.ws.command.CockpitConnectorCommandContext;
 import io.gravitee.common.service.AbstractService;
 import io.gravitee.exchange.api.command.Command;
@@ -68,7 +69,7 @@ public class WebSocketCockpitConnector extends AbstractService<CockpitConnector>
 
     @Autowired
     @Qualifier("cockpitExchangeSerDe")
-    private final ExchangeSerDe cockpitExchangeSerDe;
+    private final CockpitExchangeSerDe cockpitExchangeSerDe;
 
     @Value("${cockpit.enabled:false}")
     private boolean enabled;