FEDX-687 : GHA OSS changes to dependency_validator

[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

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

[robbecker-wf]

we can probably remove Dart 2.18 from the test matrix leaving just 2.19.6

[robbecker-wf]

QA+1 CI passes, cyclone file attached, required GHA set

[robbecker-wf]

@Workiva/release-management-p

[rmconsole-wf]

+1 from RM