Add examples

[slinkydeveloper]

We need an examples directory with ready to try projects, which contains some examples on how to use our integrations:

• An example using http with vertx Add Vertx example #195
• amqp Add AMQP example #294
• An example using http with restful ws
  • resteasy Add Quarkus example #226
  • spring boot Restful WS Spring boot example #288
• An example using kafka Created kafka example #194
• Readme that explains the examples Examples readme #298

These samples should also show how to use the event builder, how to access the event and the other basic features of cloudevents-core (maybe we need another example just showing these functionalities?).

Most of these examples can be "extracted" from the tests and the modules READMEs, we just need to clean them up and comment it.

If you're going to work on one of the examples underlined above, please write it down in the comments.

[pierDipi]

I can work on "An example using http with vertx".

[cmoulliard]

Having such examples or HowTo guides will help the developers/architects to figure out what finally they could design using CloudEvents, Java SDK.

[slinkydeveloper]

#226 adds a sample with restful-ws + quarkus