Migrate kotlin to Spring Boot 3

[mshima]

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[mshima]

@DanielFran @sendilkumarn main branch has spring-boot v2 templates with updated frontends, build-stack, and others.
Templates are in place for v3, they are renamed to v2 paths/names.
https://github.com/jhipster/jhipster-kotlin/tree/spring-boot-v3 branch has https://github.com/jhipster/jhipster-kotlin/tree/v8.0.0 integrated.
So I will let anyone guys to move forward by converting missing templates.

[DanielFran]

@asomov Are you available to contribute to the spring-boot 3 migration?
As @mshima confirmed, the blueprint is now fully migrated to v8; it just needs classes to be converted...

[asomov]

I have just changed my job, but I will do my best t or contribute. Can you please give me the direction?

[mshima]

@asomov I've added some info to contributing https://github.com/jhipster/jhipster-kotlin/blob/main/CONTRIBUTING.md#synchronizing-generator-jhipster-templates and #433
This is the first time I have touch kotlin files, so I cannot help much with the conversion.
The first spring-boot v3 conversion will not be easy, but we can implement upgrade after that.