DMS: Improve performance by synthesizing batches

## Problem

CTK is currently processing DMS events sequentially, see [io/kinesis/relay.py](https://github.com/crate/cratedb-toolkit/blob/v0.0.37/cratedb_toolkit/io/kinesis/relay.py#L105-L115). The consequence is data loading will be slow.

## Proposal

Because the ingress DMS event stream can include arbitarily-alternating event types, the data loading in CTK needs a component which synthesizes per-table batches of the same kind of DML operation before submitting them to the database.

It would be nice if this package could provide such a component, because it includes and implements relevant domain knowledge about DMS events already.