fix(docs): inconsistent docs for Google Vertex AI (#32381)

Description: Documentation is inconsistent with API docs.

Current documentation implies that to use the integration you must have
credentials configured AND store the path to a service account JSON
file.

API docs explain that you must only complete EITHER of the steps
regarding credentials.

I have updated the docs to make them consistent with the API wording.

Author: garciasces

docs/docs/integrations/chat/google_vertex_ai_palm.ipynb

@@ -45,7 +45,7 @@
     "\n",
     "### Credentials\n",
     "\n",
-    "To use the integration you must:\n",
+    "To use the integration you must either:\n",
     "- Have credentials configured for your environment (gcloud, workload identity, etc...)\n",
     "- Store the path to a service account JSON file as the GOOGLE_APPLICATION_CREDENTIALS environment variable\n",
     "\n",