Update gradle and build plugins

[JD557]

Updates Gradle to 8.9 along with the build plugins, to bring the project up to date.

As a side effect:

• There were multiple style changes in the code, due to the new version of ktlint.
• The target java version is now explicitly set to 11, this is aligned with Upgrade Android, Gradle and Kotlin versions #40
• The target android SDK version is now 33 (Android 13). This is aligned with https://developer.android.com/google/play/requirements/target-sdk
• Namespaces are now defined in the build definition, not in the manifest
• Activities need to be explicitly marked as exported (this had some extra implications on the unit test manifest)

This PR also updates the sample app to use a valid email hash (for [email protected]) and the default match provider. This way, to try out the sample app, one just needs to point it to the correct domains.

[jcazevedo]

Thanks for this!