Export Requester file to OpenAPI 3

[kylebebak]

We could add an open_api argument that can be passed to requests. This would be a dict containing OpenAPI properties (such as a description of the request, the request params, the response body structure, etc).

Only requests containing this argument would be included in the exported OpenAPI format.

For a request where no response body structure is specified, it might be nice to execute the actual request when the export function is run. This way the response could be parsed and used to determine the response body structure.

For properties belonging to the whole collection of requests, such as license information and so on, a special OPEN_API dict could be parsed from the env vars.

@jcberquist @keith-hall
What do you guys think? Worth adding? Interested in helping?