Deprecating to Jakarta EE 8

[jacekbilski]

As discussed in #705 and #729, see #729 (review), this is the first PR. The goal is to deprecate Jakarta EE 8 module and promote the Jakarta EE 9+ module.

I added Jakarta EE 9+ links in a few places where they were missing. I also fixed the links where they were still pointing to the Jakarta EE 8 module.

The examples are still using the now deprecated cloudevents-http-restful-ws module. The reason is - I cannot upgrade Quarkus or Jetty simply because next major releases, that are Jakarta EE 9+-compatible would also require Java at least 11, but we're still on 8.

[jacekbilski]

@Cali0707 My second PR is also almost ready. I did a lot of cleaning up there, Maven wrapper and plugins, documentation. I also upgraded things to their latest Jakarta EE 8-compatible versions, just to ease upgrading them to their Jakarta EE 9-compatible versions. It's just, more or less, bringing things in sync. As such, those changes might as well belong in here. Based on your proposed versioning, this could be version 4.1.1.

Please take a look at jacekbilski#1. I could extend this PR with those changes if it would make sense to you.

Because of that I also changed the title of this PR.

I also started working on the next PR. The goal there would be moving to Java 17 and upgrading everything to Jakarta EE 9-compatible versions (Spring Boot 3, Quarkus 2, etc.).