Integration with AdGuard VPN android app

[ameshkov]

Since we're launching AdGuard VPN as a separate app, we should provide advanced integration.

Note, that we're likely to add a VPN module to the app in the future. However, at first, we would like to start with an easier thing and simply provide integration.

Use cases

Detection

1. AdGuard VPN should be able to detect that AdGuard is installed and offer a way to configure the integration (IF it is not configured already)
2. AdGuard itself should be able to detect that AdGuad VPN is installed and notify the user that there's an option to use them both at the same time (IF it is not configured already)

Setup

1. Integration setup should be simple and straightforward, ideally -- done in one click;
2. It would involve some inter-process communication and needs to be established from both sides.
3. Once the integration is configured, we should show a short instruction on how it works.
4. Communication must be secure

Control

1. It should be possible to control VPN from the app (enabled/disabled)
2. There should be a shortcut from the AdGuard app to the AdGuard VPN app accessible from the main screen.
3. Custom foreground notifications for both apps should indicate that they operate in the integration mode.

Notes

• Add "AdGuard Integration" mode to the VPN app settings