bump ver to 0.4.0

bump version to v0.3.0

This release includes container infrastructure improvements and
documentation enhancements:

- Remove hardcoded container names for better scaling support
- Implement deploy:replicas pattern for worker services, preventing
  the spawning of meta container x-slurm-worker-common
- Remove privileged mode requirement and cgroup bind mounts
- Fix build cache references to use versioned tags
- Improve CI/CD retention policy (keep 5 most recent builds)
- Add SSH agent authentication troubleshooting guide

more sensible defaults

bump version

Merge pull request #24 from exactlab/7-implement-versioning

build on tag