Draft: publish: --error-on-failed to exit when signing/verifying fails
Since we have limited visibility into @CiaranG's signing server, it is hard
to make changes to the publishing process, especially ones that might break
@CiaranG's automation. So fdroid publish
mostly reports success by
moving an APK from unsigned/ to repo/. In some cases, we want immediate
failure, like in CI. So this adds --error-on-failed
for that purpose.