Add other rdkafka callbacks

[jeckhart]

• PHP version: 7.0 (but applicable to all)
• librdkafka version: 0.11.1
• php-rdkfaka version: 3.0.5

I'm hitting a problem where offsets are timing out on low traffic queues. The offsets "should" be getting committed every five minutes (using $consumer->commitAsync();) but I'm having a hard time trying to debug the issue.

rdkafka supports registering callbacks for commits, events, and other callbacks that aren't accessible in php-rdkafka today. These would be helpful to see what is happening in the async flows.

Is there a design decision to not expose those today? Would you be able to add them or be willing to review a PR?

Thank you!

[arnaud-lb]

Hi @jeckhart

I'm willing to accept a PR for this :)