File upload missing

[Ronsku]

I have a problem with file upload through formData with generated openapi-client.

• I create a new post with type 'file':

• All good in swagger UI:
  

• openapi-client generates Typescript type error "[ts] Cannot find name 'file'.":

• I resolved the type error by having "file" replaced with "File" (big F https://developer.mozilla.org/en/docs/Web/API/File) with following PR Feature/add type file #11.

• But the actual file upload still doesn't work since request headers doesn't get Content-Type: "multipart/form-data" and there is no request payload either.
  

• It should look something like this to work:
  
  

• File upload feature would be very handy to have in this openapi-client!

[mikestead]

@Ronsku Thanks for the details!

Currently I've only added / tested support for JSON (mentioned in the README).

Full multipart support shouldn't be too hard to add but I don't have a lot of time right now to work on and thoroughly test it.