The *_with_balancer suites (eg. concurrency_sharded_replication_with_balancer) run the balancer in the background for suites with sharded collections. Once the balancer also distributes unsharded collections, we should introduce new *_with_balancer suites that have unsharded collections and the balancer enabled. This should also extend the `balancerShouldReturnRandomMigrations` failpoint so that the fsm workloads will run with random moveCollection commands in the background.