Instant filters updates

[ameshkov]

The known issue with the filters updates is that background fetch is not reliable.

In order to solve this problem, we need to implement another method of pushing updates -- using remote push notifications.

This will require us to implement a push server on our side that will notify apps about a new filters update available. It will create additional server load so this will be a paid feature.

[worldsdream]

I always open the AG app and I refresh the lists. A lot of people are not doing that on their iOS devices. They do NOT get a notification that they should open up the app and check for updates. Why? We need that feature. Some users do not understand that they need to open it regularly and check for updates. They install AdGuard and open it for the first time. After that they forget or don't bother to open.

[worldsdream]

@ameshkov did the team implement such feature? To get a notification if the app did not open within 1 week for example?