minor - gcs_prefix inconsistent with readme.md

[DevanM]

GCS_PREFIX in example_values/ethereum/trace_data/values.yaml inconsistent w/ readme step 4 (ethereum-etl/streaming/last_synced_block.txt)

GCS_PREFIX should read ethereum-etl/streaming

[voron]

Yes, readme doesn't cover how to proceed with [separate] traces streaming. We need to run one more etl-streaming instance to parse traces, and it stores it's state into separate last_synced_block.txt under gs://<YOUR_BUCKET_HERE>/ethereum-etl/streaming-trace. Thus, trace_data/values.yaml is correct, as GCS_PREFIX has to be different with block_data/values.yaml.