[KOTLIN] Feature: Use linter to verify coding style

Created by: guenhter

Description

Use a linter (like klint) to verify the style of the generated Kotlin code as suggested by https://github.com/OpenAPITools/openapi-generator/pull/427#issuecomment-401612067

openapi-generator version

Next minor release

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/pull/427#issuecomment-401612067