Release binaries

[k9ert]

see #323

For now, only linux binaries get created and uploaded.

[stepansnigirev]

I cherry-picked fix the build commit to fix the build on master. Was broken by #322
Do you think it's realistic to get build jobs for osx, win and aarch64 in this PR?

[k9ert]

Gitlab provides its runner-binary for windows and MacOS. They even have publicly available windows runners. I'm not too happy to use them for security-reasons, though. Building and testing is one thing (which we're already not covering with public but a private runner) but releasing is even more security critical.

[stepansnigirev]

So if I understand this PR correctly, it will create a unix binary and upload it to your fork, right?

[k9ert]

Yes, that was wrong (fixed). Also there is documentation missing which i should put to https://github.com/cryptoadvance/specter-desktop/blob/master/docs/continuous-integration.md
Give me some more time and i'll try to create a windows-binary as well. There i have to fiddle around with picking the right runner. When i have that, maybe someone else can do the same for MacOS binaries (I don't own a Mac but can provide a windows-runner).
By the way i really think we should restrict ourself to private runners. Sooner or later we want to sign the builds (and hash them before that). Even though it might be possible on public runners, it's a very bad idea imho.