[setup] Support .gradle.kts project (#13672)
[setup] Support .gradle.kts project (#13672)

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### Checklist
- [x] I've run `bundle exec rspec` from the root directory to see all new and existing tests pass
- [x] I've followed the _fastlane_ code style and run `bundle exec rubocop -a` to ensure the code style is valid
- [x] I've read the [Contribution Guidelines](https://github.com/fastlane/fastlane/blob/master/CONTRIBUTING.md)
- [x] I've updated the documentation if necessary.

### Motivation and Context
Currently, we can write Gradle file with Kotlin that file name with `.gradle.kts`. 
But the current version of Fastlane does not support this file type.
To detect the project platform, require the setup.rb should know `.gradle.kts` is also an Android project.

https://github.com/gradle/kotlin-dsl

### Description
I add the line that `.kts` is also an Android project.
And I test with my `.gradle.kts` project.




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