Lambda handler to batch up compaction commits

[patchwork01]

Background

Split from:

• Unordered batch commit queue for compaction jobs #3686

Follows on from:

• Logic to batch up compaction commits #3904

Description

We'd like to write a lambda handler to receive compaction commit messages from SQS, and write the resulting batches to S3 and SQS with the logic from the previous issue.

Analysis

This will include a lambda handler class, and the S3 and SQS code to write and send the batches.