AvroConsumer on_commit callback

[gaisanshi]

Description

I know Consumer constructor has on_commit callback parameter. I am looking for the same callback for AvroConsumer. But I didn't find it. Should I call c function rd_kafka_conf_set_offset_commit_cb?

How to reproduce

N/A

Checklist

Please provide the following information:

• confluent-kafka-python and librdkafka version (confluent_kafka.version() and confluent_kafka.libversion()): 0.11.6,
• Apache Kafka broker version:
• Client configuration: {...}
• Operating system:
• Provide client logs (with 'debug': '..' as necessary)
• Provide broker log excerpts
• Critical issue

[rnpridgeon]

This is one of the issues I'm trying to address with the Generic Serde pr I have opened now.

#502

This won't make 1.0 but I hope to get back to it full time so we can get it merged shortly there after.

In the meantime you can actually specify this in the conf dict. This is sort of an exploit of a bug in the handling of callback configuration values but it should work as a work around in the interim.