code: public final Mono<T> log(Logger logger) {
  		return log(logger, Level.INFO, false);
  	}
docs: Observe Reactive Streams signals matching the passed filter {@code options} and
  trace them using a specific user-provided {@link Logger}, at {@link Level#INFO} level.
  <p>
  <img class="marble" src="doc-files/marbles/logForMono.svg" alt="">
  
  @param logger the {@link Logger} to use, instead of resolving one through a category.
  
  @return a new {@link Mono} that logs signals