Update library-imaginary1.2.yaml

[dianav18]

Summary

This PR adds GitHub Actions CI support for the Unikraft library package:
imaginary:1.2.

Each workflow includes:

✅ run-local: Builds and runs the unikernel locally via QEMU
✅ build: Matrix builds for QEMU and Firecracker (x86_64)
⚠️ push: Prepares OCI images for publishing (requires registry credentials)
🕒 schedule: Runs the workflow daily via cron

Test logic performs functional checks such as:

• Compiling the unikernel with kraft build
• Booting the unikernel locally with kraft run
• Verifying that the instance starts successfully
• Archiving OCI digests for registry upload

This setup improves test coverage and CI reliability by ensuring that:

• imaginary:1.2 builds cleanly for both platforms
• Local unikernel execution is validated
• Future remote registry pushes are ready once secrets are set

Note

⚠️ The push step requires REG_USERNAME and REG_TOKEN secrets
to be configured in the repository in order to push OCI images to
index.unikraft.io.

Only local tests were verified during development.

---

Checklist

• Read the contribution guidelines: https://unikraft.org/docs/contributing/unikraft
• Test run-local (QEMU) for the imaginary:1.2 library
• Validate push step with OCI secrets configured
• Add Signed-off-by to commits (git commit -s)
• Check for trailing whitespaces and ensure newline at EOF