[kotlin] implement serializable data classes (fix #8317)

[LucasKuhlemann]

Implement java.io.Serializable in kotlin data classes for kotlin-spring generator when serializableModel option is enabled.

Fixes #8317.

These existing samples clearly show the effect of this change, as they have serializableModel already set to true:

• kotlin-springboot
• kotlin-springboot-3
• kotlin-springboot-modelMutable
• kotlin-springboot-source-swagger1
• kotlin-springboot-source-swagger2
• kotlin-springboot-springfox

See the added Serializable interface on all generated models for those samples, as well as the serialVersionUID constant in each data class.

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[LucasKuhlemann]

cc
@jimschubert (2017/09) ❤️, @dr4ke616 (2018/08) @karismann (2019/03) @Zomzog (2019/04) @andrewemery (2019/10) @4brunu (2019/11) @yutaka0m (2020/03) @stefankoppier (2022/06)

[LucasKuhlemann]

Could someone please review this?

[4brunu]

Hi, can you please take a look at CI that is failing?

Perform git status
HEAD detached at pull/18386/merge
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/Category.kt
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/ModelApiResponse.kt
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/Order.kt
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/Pet.kt
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/Tag.kt
	modified:   samples/client/petstore/kotlin-spring-cloud/src/main/kotlin/org/openapitools/model/User.kt

and another one

* What went wrong:
Execution failed for task ':bootJar'.
> Error while evaluating property 'mainClass' of task ':bootJar'
   > Failed to calculate the value of task ':bootJar' property 'mainClass'.
3 actionable tasks: 3 executed
      > Main class name has not been configured and it could not be resolved

[LucasKuhlemann]

@4brunu Thanks for checking, and sorry for the late reaction.

I fixed the issue with uncommitted changes in the samples files, but I'm not sure about the second problem you pointed out. Where do you see this, or how could I try to reproduce this problem?

[4brunu]

CI is failing, here is the link.
https://github.com/OpenAPITools/openapi-generator/actions/runs/9234395104/job/25415874312?pr=18386

[LucasKuhlemann]

@4brunu Seems the issue has been fixed by someone else on the master branch, the CI no longer fails.