Support an OKHTTP backend implementation for Android

[Joannis]

This could be locked behind platform and trait. But for Android ecosystem support, OKHTTP would be a much more integrated backend for Android development.

[Lukasa]

I think having an OKHTTP based solution for Android is a good idea. I don't think we'll do exactly that here, but I have some other ideas.

[madsodgaard]

@Lukasa Just out of interest, could you share what other ideas you have?