Kafka reader should include headers when with_metadata=True

[deuscapturus]

Is your feature request related to a problem? Please describe.

I have information in the Kafka message header that I need to pass along. Currently there is no way to access message headers from pw.io.kafka.read()

Describe the solution you'd like

If with_metadata=True headers should be included in _metadata

Describe alternatives you've considered

Alternatively, with_headers: bool could be added which would add the headers to a column named _headers

[zxqfd555]

Hey @deuscapturus,

That's a nice improvement idea, we'll add it. Can you please clarify, if you use a raw/plaintext or a JSON format?