feat: add TODO for testing multiple requests in Produce stage, focusing on baseOffset and log_start_offset handling in Kafka

Author: ryan-gang

stage_descriptions/produce-05_sb8.md

@@ -38,3 +38,5 @@ The tester will also verify that the record is persisted to the appropriate log
 - Records within a batch must be assigned sequential offsets (e.g., if base offset is 5, records get offsets 5, 6, 7).
 - The response should return the base offset of the batch, not individual record offsets.
 - The official docs for the `Produce` request can be found [here](https://kafka.apache.org/protocol.html#The_Messages_Produce). Make sure to scroll down to the "Produce Response (Version: 11)" section.
+
+TODO: Send multiple request per stage from stage 5 onwards. (Need to test how baseOffset & log_start_offset are handled by kafka.)