Upgrade `flutter_foreground_task` to v2 embedding

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While running flutter pub get I get below warning:

This app is using a deprecated version of the Android embedding.
To avoid unexpected runtime failures, or future build failures, try to migrate this app to the V2 embedding.
Take a look at the docs for migrating an app: https://github.com/flutter/flutter/wiki/Upgrading-pre-1.12-Android-projects
The plugin `flutter_foreground_task` requires your app to be migrated to the Android embedding v2. Follow the steps on the migration doc above
and re-run this command.