Backfila backend client implementation to backfill a DynamoDB datastore.

There are a couple features that help keep the costs down when performing a DynamoDB datastore backfill.

This backfill client performs what should usually be a single pass of the dynamo datastore. However, in order to do that it does not provide accurate counts of the records processed but instead reports the number of segments processed instead.

This client will also by default require that the DynamoDb table has the PROVISIONED billing mode as ON_DEMAND can get very expensive otherwise.

The code is the source of truth for this client. Keep that in mind. Always refer to the code for implementation details.