Provide a starter for Jackson 2

[wilkinsona]

For those that need to use Jackson 2, it would be useful to have a starter that pulls in the dependencies that are equivalent to Spring Boot 3.5's spring-boot-starter-json.

[wilkinsona]

On second thoughts, I don't think we need this. The dependencies are already provided by the spring-boot-jackson2 module. Given its deprecated status, adding a starter as well feels too much.