fix: 🐛 forward labels parameter to Vertex AI API requests

This fix addresses the issue where the 'labels' parameter was not being
forwarded to Vertex AI API requests, preventing Google partnership labels
from being properly tracked.

Changes:
- Added 'labels' field to RequestBody TypedDict in vertex_ai.py
- Updated _transform_request_body to extract and pass labels to API
- Labels are now correctly included in the request body sent to Vertex AI

Fixes #13692

Author: miguelangelmorenochacon

litellm/llms/vertex_ai/gemini/transformation.py

@@ -495,6 +495,11 @@ def _transform_request_body(
         # Only add labels for Vertex AI endpoints (not Google GenAI/AI Studio) and only if non-empty
         if labels and custom_llm_provider != LlmProviders.GEMINI:
             data["labels"] = labels
+
+        # Add any extra body params passed to the request body
+        extra_body = optional_params.get("extra_body", {})
+        if extra_body is not None:
+            data = {**extra_body, **data}
     except Exception as e:
         raise e