add better debugging statements for vertex logging

litellm/llms/vertex_httpx.py

@@ -790,6 +790,16 @@ class VertexLLM(BaseLLM):
         if credentials is not None and isinstance(credentials, str):
             import google.oauth2.service_account
 
+            verbose_logger.debug(
+                "Vertex: Loading vertex credentials from %s", credentials
+            )
+            verbose_logger.debug(
+                "Vertex: checking if credentials is a valid path, os.path.exists(%s)=%s, current dir %s",
+                credentials,
+                os.path.exists(credentials),
+                os.getcwd(),
+            )
+
             if os.path.exists(credentials):
                 json_obj = json.load(open(credentials))
             else: