Ask user to disable battery optimization

[haveyaseen]

We should answer these questions first.

• What does this do effectively on iOS and Android?
• Is it enough to enable semi-regular polling the background?

And if it makes sense we need to create a user flow.

cc @Dionysusnu @jeroenpg

[Dionysusnu]

We should only do this if we were to actually use background polling or something else that needs it. Once we want to implement background polling, we should create the interface, not the other way around.