Transition to Dedicated Signer for Android Builds

[Ben Cooksley]

Hi all,

I have just completed transitioning the Android builds on the Binary
Factory from having the signing handled on the builders themselves (by
Qt's Android Tooling) to a dedicated signing machine (using Android's
tooling directly).

Should there be any issues please let me know.

This has improved the overall security and scalability of the Binary
Factory, ensuring that high value assets such as our signing keys are
kept separate from the builds themselves.

As part of this the F-Droid repository on cdn.kde.org will also be
automatically updated going forward.

For now this is pointed to a test path - if someone could please
confirm that the repository at https://cdn.kde.org/android/test/ is
working correctly, that would be appreciated (after which i'll switch
it to the production path).

(Side note: it appears we are producing APKs marked for debugging,
which F-Droid isn't 100% happy with)

Thanks,
Ben