[feature request] Support Consumer.getLastMessageId

First off, thank you for all the development you do on Pulsar! :smile:

### Motivation

When combining data from two Consumers by event timestamps and the topics have significant backlog, it gets tricky to make sure that all relevant events have arrived. If we could check from the Consumer whether we have already read the latest message, that would simplify the code.

The C++ client already supports Consumer.getLastMessageIdAsync. (Though the Java client has deprecated the singular version of that method, supposedly due to the Consumers being able to subscribe to several topics concurrently. For us right now the singular version is enough.)

Inizia ispezionando la Consumer API nel repository pulsar-client-node e il supporto esistente di getLastMessageIdAsync nel client C++. Aggiungi quindi il metodo Consumer richiesto per il client Node e verifica che indichi se l'ultimo messaggio è stato letto, includendo la copertura per i consumer con un arretrato significativo.

Scritto dal modello di indicizzazione a partire dal testo della issue.