[REQ] RestTemplate support for Spring boot 3

Created by: kevinparaport

Is your feature request related to a problem? Please describe.

With the release of Spring Boot 3, it now uses JDK 17 and Spring Web 6. If you try using a Spring Boot 3 server with resttemplate generated client, it doesn't work because of some breaking changes with headers.

Describe the solution you'd like

The Spring Boot server generator uses a flag "useSpringBoot3", it'd be nice if we had that option with the Spring related clients (e.g. resttemplate and webclient)

Describe alternatives you've considered

Manually upgrading to Spring 6 when generating the client.

Additional context

N/A