Add compileOptions to fix new flutter release warning

[tun43p]

What do these changes do?

I've updated the sourceCompatibility and targetCompatibility for Java in the build.gradle file.

Why are these changes necessary?

These changes are necessary since Flutter has updated its version and we have a warning in the console. Without this change, we can't update the configuration.

You are applying Flutter's app_plugin_loader Gradle plugin imperatively using the apply script method, which is deprecated and will be removed in a future release. Migrate to applying Gradle plugins with the declarative plugins block: https://flutter.dev/go/flutter-gradle-plugin-apply

You are applying Flutter's main Gradle plugin imperatively using the apply script method, which is deprecated and will be removed in a future release. Migrate to applying Gradle plugins with the declarative plugins block: https://flutter.dev/go/flutter-gradle-plugin-apply

How did you verify these changes?

I used my package instead of the pub.dev one.

✓ Built build/app/outputs/flutter-apk/app-staging-debug.apk

Anything else a reviewer should know?

I'm open to discussion if you need more information.

[rlepinski]

This looks good to us, we probably want to set a kotlin version as well. Thank you for the PR, we will try to get it merged this coming week

[crow]

Going to merge this and add a couple remaining bits before we do a release. Thanks again for the PR