Provide Process Groups with a FlowFile Concurrency level for transferring a batch of FlowFiles at once

NIFI-7476 provides the ability for a Process Group to bring in a single FlowFile at a time instead of continually streaming data. It also provides the ability to output data as a batch. If a Process Group outputs the data in a batch, another Process Group should have the ability to pull in all of that data in a single batch as well.