Use Jackson 3 by default in the Jersey starter

[khopland]

eThe Jersey starter currently uses Jackson 2, so Jersey responses do not use Spring Boot’s default Jackson 3 mapper and configuration.

This change upgrades Jersey to 4.0.3 and uses Jackson 3 by default. Jackson 2 remains available through spring.jersey.preferred-json-mapper=jackson2 like other starters. The preference applies to application and Actuator endpoints, including when Jackson features are already registered.

Adds tests for both mapper versions and Actuator configurations. Jersey module, starter, smoke, and Actuator integration checks pass.

Closes #51931

[khopland]

Oh, I didn’t notice #51935 had already been opened when I created this PR.

Both PRs upgrade Jersey to 4.0.3 and make Jackson 3 the default. With #51935, you switch back to Jackson 2 by replacing dependencies. Here, both versions are included, and you can choose with spring.jersey.preferred-json-mapper, even if the application has already registered Jackson features.

I also added tests for Actuator-only applications and separate management ports. In local testing, an Actuator-only app using spring.jackson.property-naming-strategy=SNAKE_CASE with mapper isolation disabled returned firstName with #51935 and first_name with this PR. A custom EndpointJsonMapper worked on both ports here, but only on the main port with #51935.

Supporting both providers makes this PR bigger. I’m happy to simplify it so switching to Jackson 2 requires replacing dependencies, while keeping the Actuator fixes and regression tests.

[khopland]

A question i have is how a user should select what jackson version jercey should use, i have added the prop spring.jersey.preferred-json-mapper, but it could also be done with dependecy exlusion. And a other question is if it is a breaking change to change the dafault jackson version in jercey starter for the user?