Convert the build.gradle to build.gradle.kts

[Valefant]

We want to use Kotlin for describing the build.gradle file as it will be simpler to maintain in the future.

This is a good resource when working on this issue
https://guides.gradle.org/migrating-build-logic-from-groovy-to-kotlin/

[Valefant]

This is going to be implemented with the upcoming issue #21.