Support postman collection input

[mquan]

Use https://github.com/joolfe/postman-to-openapi to convert from postman to OpenAPI Spec.

🚫 Blockers:

1. schema types in raw body aren't inferred. Project isn't maintained, the following issues have been opened for 6months+ https://github.com/joolfe/postman-to-openapi/pull/237 https://github.com/joolfe/postman-to-openapi/issues/246

2. Even after above hurdle there's no way to tell if a parameter is required or not

Both stem from postman collection being a bad standard to store API spec