[KOTLIN] Kotlinx serialization, use first party retrofit converter factory

[larst-ingka]

Requirement #18593

What has changed:
Switched out the retrofit converter factory used for kotlinx_serialization in the kotlin generator with the new first party converter.

• Dependency changed com.jakewharton.retrofit:retrofit2-kotlinx-serialization-converter -> com.squareup.retrofit2:converter-kotlinx-serialization in modules/openapi-generator/src/main/resources/kotlin-client/build.gradle.mustache
• Import changed com.jakewharton.retrofit2.converter.kotlinx.serialization.asConverterFactory -> retrofit2.converter.kotlinx.serialization.asConverterFactory in modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/infrastructure/ApiClient.kt.mustache

Why was it changed:

Given that no further development is to be expected on the deprecated repository, and the fact that the repo was moved to a first party converter with no code changes between.

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Technical committee mentions

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

[4brunu]

Looks good to me 👍