Switch to hosting files on github.

[taylorhadden]

AWS egress fees are starting to add up. Time to switch to using GitHub as the primary update server

[taylorhadden]

There is a requirement to use tags named "vX.X.X", which is very annoying. This is not very monorepo friendly.

It would be nice if the tag prefix were configurable.

[taylorhadden]

This could be resolved by electron-userland/electron-builder#9216