RFC: Including Kafka receiver/exporter support in Lambda build

[mheffner]

Opening this issue to see if there's interest in including Kafka support in a Lambda Extension build. We've excluded Kafka support because the dependencies are quite large (ie. rdkafka) and receiving from Kafka in a Lambda environment does not seem common.

Exporting from a Lambda to Kafka could be a use case, but interested in getting feedback if users find this a necessary use case. We could do a separate lambda release with Kafka support for this if so.

Please comment below if this is useful!