Document Kafka headers added by zilla ex:`zilla:*`

[vordimous]

Find the kafka headers that zilla creates for each binding in the specs and document which are created:
https://github.com/aklivity/zilla/blob/develop/specs/binding-grpc-kafka.spec/src/main/scripts/io/aklivity/zilla/specs/binding/grpc/kafka/streams/kafka/produce/bidi.stream.rpc/client.rpt#L32

document parameters from headers as well eg: ${params.headerX}