[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.)

Beginne mit der Untersuchung der Consumer API im Repository pulsar-client-node und der Unterstützung von getLastMessageIdAsync im bestehenden C++-Client. Füge anschließend die angeforderte Consumer-Methode für den Node-Client hinzu und überprüfe dann, ob sie meldet, ob die neueste Nachricht gelesen wurde, einschließlich einer Abdeckung für Consumer mit erheblichem Rückstand.

Vom Indexierungsmodell aus dem Issue-Text verfasst.