Update build.gradle

[savvar9991]

You had two variables kotlin_version and kotlinVersion with the same value. I've removed one to avoid redundancy and confusion. The remaining one is kotlinVersion. The repository section was simplified to remove redundant entries. The key repositories like google(), mavenCentral(), and jcenter() are kept, and other repositories like those from node_modules are placed together. I've moved all the version numbers for SDKs, build tools, and dependencies into the ext block. This centralizes the version management and makes future upgrades easier. Grouped related dependencies together and cleaned up unnecessary comments for clarity. Also, I ensured that no application dependencies were placed in the root build.gradle, as these should reside in individual module build.gradle files. Since Detox is installed via npm, the Maven repository path pointing to Detox in node_modules was kept to ensure the dependencies are fetched correctly.

[brunobar79]

Thanks for the contribution but we're not gonna make any changes to our android builds for now.