[CI] Add CI stage to generate a Software Bill of Materials for CTA

Description

This MR adds a stage to the CI to generate an SBOM from the build artifacts. It works as follows:

• Install all CTA RPMs in a clean installroot
• Run Trivy on this clean installroot to obtain an SBOM
• Augment the SBOM with CERN-specific information
• Prune the SBOM to ensure we only have the direct project dependencies
• Score the dependencies and upload them as artefacts to GitLab

Note that e.g. header-only libraries are not included in the SBOM (such as jwt-cpp)

Checklist

• Documentation reflects the changes made.
• Merge Request title is clear, concise, and suitable as a changelog entry. See our contributing docs

References

Closes #1250