Update to gitlab-ci 0.8.0
Updates horizon-spec to use gitlab-ci 0.8.0 with the new modular configuration structure.
Changes
- Update gitlab-ci-omnix input from 0.5.0 to 0.8.0 (using nix/gitlab-ci repository)
- Update .gitlab-ci.yml remote from 0.3.0 to 0.8.0
- Migrate nix/ci.nix to new modular configuration:
- Move omnix config from gitlab.ci.omnix to gitlab.ci with imports
- Split cachix configuration into separate module
- Use gitlab.ci.imports for modular CI configuration
This brings horizon-spec up to date with the latest gitlab-ci version.