Support locking documents in ReactiveFindByIdOperation

[aaronjwhiteside]

API Idea:

   final MyEntity entity = template.findById(MyEntity.class)
      .lock(Duration.ofSeconds(5))
      .one("abc123");

.lock() should also exist that takes no arguments and uses the default lock duration.

[mikereiche]

TODO: use getAndLock(id, duration)