Improvements to distribution packages

[straight-shoota]

• Alert users of new deb and rpm repositories
• Add nightly and unstable channels ([CI] Publish nightly builds to OBS #10684)
• Automatic release trigger via webhook (if we want that?)
• Separate shards package
• Add docs and samples packages for deb
• Add Arch Linux to OBS
• Explore Dockerimage distribution on OBS (probably not a good solution for us because it builds scratch images with full root file system)
• Write guide on how to publish a Crystal application with OBS

[jhass]

I see no reason to add Arch Linux to OBS. We're in the official repositories and there's a crystal-git in the AUR. If you want to provide a binary nightly package that should happen via the AUR. Adding custom repositories is very uncommon.

[straight-shoota]

Okay. I just figured it would be really easy to build from the same sources as the deb and rpm packages. But when it's not necessary, we don't have to worry about that.