Change the naming scheme of the installers at build time

We'd like to have all produced installers follow a similar naming scheme, for example:

mullvad-browser-{platform}-{version}.{extension}

So for example with Mullvad Browser 12.0.6, we would have:

• mullvad-browser-windows-12.0.6.tar.xz
• mullvad-browser-linux64-12.0.6.tar.xz
• mullvad-browser-macos-12.0.6.tar.xz