Document how to play with app next and backend. Disable the extensions not available. #23979

Signed-off-by: cmoulliard <cmoulliard@redhat.com>

packages/app-next/README.md

@@ -1,3 +1,7 @@
 # example-app-next
 
-This package is an example of a Backstage application.
+This package is an example of a Backstage application using the [new frontend](../../docs/frontend-system/index.md).
+
+To play with it, open a terminal and run the command: `yarn start`
+
+**Note**: Don't forget to open a second terminal and to launch the backend or [backend-next](../../docs/backend-system/index.md) application using `yarn start` too command !

packages/app-next/app-config.yaml

@@ -10,7 +10,7 @@ app:
 
   extensions:
     # - apis.plugin.graphiql.browse.gitlab: true
-    - graphiql-endpoint:graphiql/gitlab: true
+    # - graphiql-endpoint:graphiql/gitlab: true
 
     # Entity page cards
     - entity-card:catalog/about
@@ -18,7 +18,7 @@ app:
     - entity-card:catalog/links:
         config:
           filter: kind:component has:links
-    - entity-card:linguist/languages
+    # - entity-card:linguist/languages
     - entity-card:catalog-graph/relations:
         config:
           height: 300