Allow for forest locking in the query

[BillFarber]

As a connector,
I want to have multiple copies of the kafka-marklogic-source running,
So that I can pull documents out of MarkLogic as fast as possible.

Given documents that are in the "ready" collection,
When the connector queries the database in update mode (for setting the collection to "processing",
Then the connector doesn't lock the entire set of documents,
and the connector only queries a subset of forests,
and the connector only locks the target documents in those forests.

Use a synthetic semaphore to lock the queried documents in a subset of forests.