location should not be optional when using Google Vertex.

Also, update `GoogleVertexLLMService` initialization pattern in the example file.

src/pipecat/services/google/gemini_live/llm_vertex.py

@@ -49,7 +49,7 @@ class GeminiLiveVertexLLMService(GeminiLiveLLMService):
         *,
         credentials: Optional[str] = None,
         credentials_path: Optional[str] = None,
-        location: str = "us-east4",
+        location: str,
         project_id: str,
         model="google/gemini-2.0-flash-live-preview-04-09",
         voice_id: str = "Charon",

src/pipecat/services/google/llm_vertex.py

@@ -137,6 +137,10 @@ class GoogleVertexLLMService(OpenAILLMService):
         if project_id is None:
             raise ValueError("project_id is required")
         if location is None:
+            # If location is not provided, default to "us-east4".
+            # Note: this is legacy behavior; ideally location would be
+            # required.
+            logger.warning("location is not provided. Defaulting to 'us-east4'.")
             location = "us-east4"  # Default location if not provided
 
         base_url = self._get_base_url(location, project_id)