feat(firebase_app_check): provide `androidDebugProvider` boolean for android debug provider & update app check example app

[russellwheatley]

Description

Once this has been approved, I'll look to update the android documentation here.

Related Issues

closes https://github.com/firebase/flutterfire/issues/6551

Checklist

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• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ ] My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• [ ] All existing and new tests are passing.
• [ ] I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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[russellwheatley]

We probably should look to create an option for users to choose between the two different android providers as well (Safety Net and Play Integrity) which this PR attempted to implement