Jakarta 11, Spring Boot 4

[jacekbilski]

This is the fourth PR of the series towards Java 17 / Spring Boot 4 / Quarkus 3 / Jakarta EE 11.

We're finally on Jakarta 11 and are using Spring Boot 4 and Jackson 3. I migrated most samples and tests to use Jackson 3, but left some just to show, that Jackson 2 is still here. Feel free to disagree, I could migrate everything else.

Two notes/questions though:

1. I implemented Jackson 3 beside Jackson 2 module and named it io.cloudevents.formats.jackson3. That way we're not forcing anyone to migrate to Jackson 3, for a time being they can use Jackson 2. But the naming means we'll have this "3" dangling at the end for quite some time, until Jackson 4 comes out or is completely replaced by something else. The other option could be to rename current jackson module to jackson2 and name the new one jackson. But that would be a breaking change, people will get confused. One other, even more drastic, option would be to completely drop Jackson 2 and leave Jackson 3. But Jackson 2 still lives, has its LTS versions released. I guess, that would be too far-going. What's your opinion on this?
2. This PR doesn't include migrating to JSpecify. It's a project on its own, I'm still working on this and hope to be able to prepare a new PR soon. If you'd like to wait for it before releasing this PR - fine by me. But I anyway thought that reviewing those two separately would also make thing easier.