FEDX-689 : GHA OSS changes

[alishadalal-wk]

Summary

Finish migration to GHA.

• Remove Dockerfile
• Remove skynet.yaml
• Generate an SBOM (see the guide)

Testing

• CI passing
• cyclone DX file attached as an artifact on the GHA build

[aviary-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.