Support for kinesis handler "concurrent batches per shard"

In addition to the batch_size and batch_window currently supported for kinesis handlers, it would be nice to support the "Concurrent batches per shard" trigger configuration parameter.

Start by locating the Kinesis handler configuration that implements batch_size and batch_window, then trace how those settings become the AWS trigger configuration. Done means the Concurrent batches per shard parameter can be configured alongside the existing settings, with corresponding coverage for the handler configuration.

Written by the indexing model from the issue text.