Transform the items emitted by an Observable into Observables, and mirror those items emitted by the
most-recently transformed Observable.
The flatMapLatest operator is similar to the flatMap and concatMap methods described above, however, rather than
emitting all of the items emitted by all of the Observables that the operator generates by transforming items
from the source Observable, flatMapLatest instead emits items from each such transformed Observable only until
the next such Observable is emitted, then it ignores the previous one and begins emitting items emitted by the
new one.