Update to non-obsolete libraries and APIs; do not depend on the Schema Registry; bundle certificate and schemas

[lszrn]

This project is using obsolete libraries and APIs.

For a consumer, I would recommand kafka-python-ng and fastavro.

It could also use the following enhancements:

• a CHANGELOG.md
• a ca.pem bundled to let the example work "out-of-the-box"
• the bundled schemas for both key and value to avoid a dependency on the Schema Registry
• a railnova-kafka-example.py that can be copy-pasted to bootstrap a client's project
• a pyproject.toml file for a simpler installation procedure (ie: as a module)

[lszrn]

Eventually, I kept the dependency on confluent-kafka, better specified and upgraded to the latest version.