location should not be optional when using Google Vertex.

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

examples/foundational/14p-function-calling-gemini-vertex-ai.py

@@ -76,9 +76,8 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
 
     llm = GoogleVertexLLMService(
         credentials=os.getenv("GOOGLE_VERTEX_TEST_CREDENTIALS"),
-        params=GoogleVertexLLMService.InputParams(
-            project_id=os.getenv("GOOGLE_CLOUD_PROJECT_ID"),
-        ),
+        project_id=os.getenv("GOOGLE_CLOUD_PROJECT_ID"),
+        location=os.getenv("GOOGLE_CLOUD_LOCATION"),
     )
     # You can aslo register a function_name of None to get all functions
     # sent to the same callback with an additional function_name parameter.