Update import_files_example.py to optionally use import_result_sink to show import result status in a written GCS file. (GoogleCloudPlatform#13310)

* Update rag import_files_example to optionally use import_result_sink to demonstrate this feature

* Update rag import_files_example to optionally use import_result_sink to
demonstrate this feature to users.

---------

Co-authored-by: Ed Tsoi <edtsoi@google.com>

Author: edtsoi430

generative_ai/rag/import_files_example.py

@@ -43,6 +43,7 @@ def import_files(
         transformation_config=rag.TransformationConfig(
             rag.ChunkingConfig(chunk_size=512, chunk_overlap=100)
         ),
+        import_result_sink="gs://sample-existing-folder/sample_import_result_unique.ndjson",  # Optional, this has to be an existing storage bucket folder, and file name has to be unique (non-existent).
         max_embedding_requests_per_min=900,  # Optional
     )
     print(f"Imported {response.imported_rag_files_count} files.")