Add to proposed tooling

[arlemi]

Work had been started on an official support for converting collections to OpenAPI 3, we might want to use that as a base, or contact @VShingala to see where the project is too!

Cf. postmanlabs/openapi-to-postman#312

[VShingala]

Yeah, we had done significant work on this under this branch of https://github.com/postmanlabs/openapi-to-postman repository.