refactor: rewrite create-app-auth-client mutation as REST endpoint

packages/backend/test/mocks/rest/api/v1/admin/apps/create-auth-client.js

@@ -0,0 +1,17 @@
+const createAppAuthClientMock = (appAuthClient) => {
+  return {
+    data: {
+      name: appAuthClient.name,
+      active: appAuthClient.active,
+    },
+    meta: {
+      count: 1,
+      currentPage: null,
+      isArray: false,
+      totalPages: null,
+      type: 'AppAuthClient',
+    },
+  };
+};
+
+export default createAppAuthClientMock;