Add .kotlin/ to gitignore (#48598)

Summary:
Adding .kotlin to gitignore. This folder starts to get used with K2 (with Kotlin 2.0) so we should be
adding it to the gitignore files

## Changelog:

[INTERNAL] - Add .kotlin to gitignore

Pull Request resolved: https://github.com/facebook/react-native/pull/48598

Test Plan: N/A

Reviewed By: cipolleschi

Differential Revision: D68018000

Pulled By: cortinico

fbshipit-source-id: 78be3597071d07d105145d8ba94cd83cbf4f21bc