organize the supported features section

[sparty02]

Organizing for readability and a better "at a glance" understanding of the state of what this SDK supports. As a follow-up, I'd like to propose re-organizing the maven modules under "protocols" and "formats" modules, but I can address that in a different PR if you agree with that change, which would look something like this:

├── api
├── benchmarks
├── bom
├── core
├── docs
├── examples
│   ├── amqp-proton
│   ├── basic-http
│   ├── kafka
│   ├── restful-ws-quarkus
│   ├── restful-ws-spring-boot
│   ├── spring-function
│   ├── spring-reactive
│   ├── spring-rsocket
│   └── vertx
├── formats
│   ├── avro
│   ├── json-jackson
│   └── protobuf
├── protocols
|   ├── amqp
|   ├── http
|   │   ├── basic
|   │   ├── restful-ws
|   │   ├── restful-ws-integration-tests
|   │   └── vertx
|   ├── kafka
├── spring
└── sql