[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.)

Comienza inspeccionando la Consumer API en el repositorio pulsar-client-node y el soporte existente de getLastMessageIdAsync en el cliente C++. Añade después el método Consumer solicitado para el cliente Node y verifica que indique si se ha leído el mensaje más reciente, incluyendo cobertura para consumidores con un backlog significativo.

Escrito por el modelo de indexación a partir del texto del issue.