API v0.2 (external), builder file config

[dvush]

• implements api v0.2 (inputs and outputs)
• builders are configured with a yaml file

📝 Summary

⛱ Motivation and Context

📚 References

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✅ I have run these commands

• [ ] make lint
• [ ] make test
• [ ] go mod tidy
• [ ] I have seen and agree to CONTRIBUTING.md