Update dependencies and build tools

[MatsG23]

No description provided.

[MatsG23]

Should we for now use

app_settings:
    git: https://github.com/spencerccf/app_settings.git

in pubspec.yaml as a temporary fix until version 4.3.0 is published?

[nucleus-ffm]

If that works without any problems, we can do that. We just use the plugin for a button in the settings to open the Android notification settings. Maybe we can even remove the plugin and replace it with a platform-specific call.

[MatsG23]

If we would implement opening this specific settings page as a platform-specific call, the bundle size would also be reduced a bit (one less plugin).
In the WelcomeView, we do already open the settings page for adding a battery excemption for the app using a platform-specific call. Doing the same for the notifications may be very similar to the short code we use for that.
https://github.com/nucleus-ffm/foss_warn/blob/main/android/app/src/main/kotlin/de/nucleus/foss_warn/MainActivity.kt#L42

[MatsG23]

The platform-specific call for Android is finished. But I cannot test it right now because of flutter/flutter#128204

[nucleus-ffm]

looks good and works as expected. We can merge the branch from my side.