Allow sending columns with raw bytes in the python connector

[lewymati]

Is your feature request related to a problem? Please describe.
Cannot stream a table with multiple columns via a Python connector, when one of them is of type bytes. For example:

message = {"col1": "foo", "col2": some_bytes}
self.next_json(message)

doesn't work as bytes are not json serializable.
self.next_bytes is not useful as well as it expects bytes encoded json string.

Some workaround is to use base64 to serialize/deserialize, but it's not ideal.