refactor(frontend-app-api): rephrase root overriding error message

Signed-off-by: Camila Belo <camilaibs@gmail.com>

packages/frontend-app-api/src/wiring/createApp.test.tsx

@@ -68,7 +68,7 @@ describe('createInstances', () => {
       }),
     ];
     expect(() => createInstances({ config, plugins })).toThrow(
-      'The following plugins are overriding root extensions and root extensions cannot be overridden: plugin',
+      "The following plugin(s) are overriding the 'root' extension which is forbidden: plugin",
     );
   });
 

packages/frontend-app-api/src/wiring/parameters.ts

@@ -206,7 +206,9 @@ export function mergeExtensionParameters(options: {
       .filter(({ id }) => id === 'root')
       .map(({ source }) => source.id);
     throw new Error(
-      `The following plugins are overriding root extensions and root extensions cannot be overridden: ${rootPluginIds}`,
+      `The following plugin(s) are overriding the 'root' extension which is forbidden: ${rootPluginIds.join(
+        ',',
+      )}`,
     );
   }