Rollback to stable was modified in WT-10743 to queue work which is then consumed by worker threads. This is a useful optimization but makes testing rollback to stable deterministically harder. We should provide configuration to rollback to stable that defines whether or not it is singly threaded.

Acceptance criteria:

• Add a new config string to the rollback to stable API that turns off the multithreaded mode.
• Find a way to test that providing this string does in fact stop the threads from being created. This may need to be a unit test. Once this test is created test both on and off configurations.