Upgrade to Jetty 12

[zUniQueX]

This PR provides an early preview of the Jetty 12 upgrade with Jetty 12.0.0.beta1.

Jersey 3.1.x currently has compatibility issues with Jetty. Jersey 3.1 is compatible with Jakarta EE 10 and therefore uses servlet-api 6. But the current Jetty version 11.0.x isn't compatible with servlet-api 6.

Although the upgrade to Jetty 12 is a major upgrade, this can be released for the servlet compatibility in Jersey 3.1.x IMHO.

Notable changes:

• The servlet-api isn't integrated into Jetty's core classes any more and rather moved out to a separate module. For servlet classes the correct servlet module has to be included (e.g. jetty-ee10-servlet for Jersey 3.1).
  The JettyHttpContainer is rewritten by removing all servlet related classes. This prevents incompatibilities with future servlet versions.
• The Handler interface has changed and now uses a Callback class to signal output completion. The handled state is set with the method's return value.
• JettyHttpContainer: The SecurityContext is set via the AuthenticationState. In the current implementation no SecurityHandler is provided and therefore the AuthenticationState will always be null. Maybe the JettyHttpContainer should implement the Handler.Singleton interface to let users specify a SecurityHandler.