Make Sentry Extension Public for Kotlin DSL Compatibility

[vlh-ioki]

This pull request addresses the visibility issue of the Sentry Extension when using Kotlin DSL. Previously, the extension was not accessible in Kotlin DSL due to its visibility constraints.

Changes include:

1. Updated the Sentry Extension to be public, allowing it to be accessed and utilized in Kotlin DSL scripts.
2. Refactored the existing Groovy DSL scripts to Kotlin DSL for consistency and to ensure compatibility with the updated Sentry Extension.
3. Updated the test cases to reflect the changes and ensure that the updated Sentry Extension works as expected with Kotlin DSL.

These changes will improve the plugin's compatibility with Kotlin DSL and provide a more flexible and consistent configuration experience for users.

[StefMa]

Nice hit!
Thank you very much!

Please drop the increase version commit.
This shouldn't be here 🙃 .

Rest looks good 👏