`kafkajs` API differences: `on`, `events`, `Partitioners`

[silverwind]

Following MIGRATION.md, I notice at least these differences from the kafkajs API which are not documented there. Feel free to close if you are not planning to implement a fully compatible API.

1. producer.on is absent (to register for producer events)
2. producer.events is absent (I'm using producer.events.CONNECT, producer.events.DISCONNECT, producer.events.REQUEST_TIMEOUT)
3. Partitioners export is absent (I'm using Partitioners.DefaultPartitioner)

[theo-bulfon-wmx]

Instrumentation Events were usefull.
I hope you will implement it.

consumer.on('consumer.group_join', () => {
   // DO SOMETHING
 });

Thank you for all the job done so far.

[troch]

Hello, I also use on('consumer.group_join') from KafkaJS to know when partition assignment has changed. There is consumer.assignment() to get assigned partitions, but I'd need to know when it changes. Thanks!

[Jamesgt]

A partial solution might be #287