Reactor Kafka 1.0.0.M4

This is the MILESTONE 4 release of Reactor Kafka 1.0.0.

This milestone has upgraded Reactor Kafka to use Reactor Core version 3.1.0.RC1.

There are no major API changes in this release.

✨ New features and improvements

• Support for transactional sends and exactly once delivery (ad1fa17)
• Header support to Sender and Receiver records (883f7a9)

⚠️ Update considerations

• This release is compatible with reactor-core version 3.1.0.RC1.

👍 Thanks to the following contributors who participated in this release

@rajinisivaram @smaldini