Fix service account for firebase prod. (#8422)

Co-authored-by: Sarah Rainsberger <[email protected]>

src/content/docs/en/guides/backend/google-firebase.mdx

@@ -145,9 +145,19 @@ const serviceAccount = {
   client_x509_cert_url: import.meta.env.FIREBASE_CLIENT_CERT_URL,
 };
 
-export const app = activeApps.length === 0 ? initializeApp({
-  credential: cert(serviceAccount as ServiceAccount),
-}) : activeApps[0];
+const initApp = () => {
+  if (import.meta.env.PROD) {
+    console.info('PROD env detected. Using default service account.')
+    // Use default config in firebase functions. Should be already injected in the server by Firebase.
+    return initializeApp()
+  }
+  console.info('Loading service account from env.')
+  return initializeApp({
+    credential: cert(serviceAccount as ServiceAccount)
+  })
+}
+
+export const app = activeApps.length === 0 ? initApp() : activeApps[0];
 ```
 
 :::note