Create per arch .apks from build

As per

https://gitlab.com/fdroid/fdroiddata/-/merge_requests/24694#note_2859310169

Fdroid is asking that we split our 250mb .apk file full of code for 4 arches into 4 seperate .apks and sign each one and publish those as easier for users to download. As this app is largely native code, that 250mb is mostly (75%ish) redundant copies of native builds of arti and onionmasq, so it makes sense for both users and distribution.

I aim to start scoping this at the start of the week.

If we're aiming for our timeline with release on this platform then complicatedly we might want to figure this work out for a 1.3.x branch that we can build and publish on dist.tpo with minimal change but build tooling while 1.4.0 work continues elsewhere, so I might also start with branching from 1.3.0 for this, and merge it up later when working and done