Description

When setting the response type as type: string and format: binary, the return type is generated as file, even though the documentation states that file is no longer a data type in OpenAPI 3.0, as mentioned here: https://swagger.io/docs/specification/data-models/data-types/#file

format: byte is correctly generated as bytearray.

This becomes a problem for us as we use custom templates to set the return type of functions ({{#returnType}} -> {{.}}{{/returnType}}), which will result in file, which is not valid in python, meaning the resulting generated code does not run.

openapi-generator version

Tested with 4.1.3, as well as these snapshots:
openapi-generator-cli-4.2.1-20191104.150105-22
openapi-generator-cli-5.0.0-20191024.154544-16

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Python binary response
  version: 1.0.0
paths:
  "/foo":
    post:
      responses:
        "200":
          description: "Success"
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary

Command line used for generation

java -jar openapi-generator-cli-4.1.3.jar generate -g python-flask -i openapi.yml

Steps to reproduce

1. Copy yaml above to openapi.yml
2. Run java -jar openapi-generator-cli-4.1.3.jar generate -g python-flask -i openapi.yml
3. openapi_server/controllers/default_controller.py now contains a single function, with :rtype: file

Related issues/PRs

None which I could find

Suggest a fix/enhancement

I am unfamiliar with the code base, but what I could find was that here the type file is declared as a primitive of Python, which I don't think is the case. It also maps file to file. Presumably this should map to something like str or bytearray.