Add NotConfiguredException with a better error message than provided by the server

Author: emilypgoogle

firebase-ai/src/main/kotlin/com/google/firebase/ai/common/APIController.kt

@@ -334,6 +334,9 @@ private suspend fun validateResponse(response: HttpResponse) {
   if (message.contains("The prompt could not be submitted")) {
     throw PromptBlockedException(message)
   }
+  if (message.contains("genai config not found")) {
+    throw NotConfiguredException(message)
+  }
   getServiceDisabledErrorDetailsOrNull(error)?.let {
     val errorMessage =
       if (it.metadata?.get("service") == "firebasevertexai.googleapis.com") {

firebase-ai/src/main/kotlin/com/google/firebase/ai/common/Exceptions.kt

@@ -89,6 +89,16 @@ internal constructor(
 internal class UnsupportedUserLocationException(cause: Throwable? = null) :
   FirebaseCommonAIException("User location is not supported for the API use.", cause)
 
+/**
+ * The user's project does not have the Gemini Developer API enabled in the Firebase Console.
+ *
+ * See the Firebase documentation for the
+ * [steps](https://firebase.google.com/docs/ai-logic/faq-and-troubleshooting?api=dev#error-genai-config-not-found)
+ * to enable the Gemini Developer API.
+ */
+internal class NotConfiguredException(cause: Throwable? = null) :
+  FirebaseCommonAIException("Gemini Developer API not enabled in Firebase console.", cause)
+
 /**
  * Some form of state occurred that shouldn't have.
  *