[REQ][KOTLIN-SPRING] Support jakarta namespace for kotlin-spring generator

Created by: estigma88

Support jakarta namespace for kotlin-spring generator.

kotlin-spring generator uses javax.* namespaces, and we cannot configure it to use jakarta.* namespaces.

Describe the solution you'd like

Use a similar approach we have for JavaSpring, where there is a flag named useSpringBoot3, and later, used inside the mustache template to switch to jakarta namesespaces, as you can see here.

Describe alternatives you've considered

Overriding the mustache files somehow in my project to use jakarta.* namespace

Additional context

Spring Boot 3 is going to be released in November and will only support jakarta.* namespaces, so, this is a blocker to upgrade