Problem: After a recent switch to GitHub Actions, job that creates
prerelease suddenly stopped working.
Solution: Switch to the autoreleasing script from serokell.nix
which uses 'gh' instead of 'hub'.
Problem: For historical reasons some Serokell projects use niv to
organize nix-related dependencies. However, the majority of other
projects in our company use nix flakes to organize these dependencies.
Solution: Add flake and provide ci attibutes as flake outputs.
