9.4.0-beta.1

Changes

• Use Kafka with Schema Registry @iancooper (#2430)
• Pulls in Json.NET and NJsonSchema as dependencies to allow us to mark up Command/Event base classes
• This dependency comes from Confluent's dotnet Kafka library, but may be useful to those still using Json.NET over System.Text.Json
• It does create additional 'core' dependencies, and new attributes to support these libs, hence the minor version bump here.