Upgrade to RESTEasy 4

Current development branch (6.2) uses RESTEasy 3.8.0.Final.

Recommended upgrade:

• RESTEasy 4.4.2.Final
• Make sure we stay aligned with the Jackson version property in the POM above, 2.10.1 for now.

For the lack of meaningful aggregated Release Notes, see this old blog post RESTEasy 4 is coming soon for an overview (in a nutshell major cleanup, code restructure and optimizations, microprofile and quarkus support), and section 59.4. Migration to RESTEasy 4 series of the user guide.