title: drf_yasg: How to define multipart/form-data in request body
body: <h1>Not able to generate a swagger file with multipart/form-data content-type in request</h1>
  <h2>Description</h2>
   I have a POST request to upload a document where I send the document sent in multipart/form-data. I have tried to describe the form data as such
  <p><img src="https://user-images.githubusercontent.com/54931201/150966253-be4f6f71-7dd5-4fb0-90b6-a21796aa9692.png" alt="image" /></p>
  <p>This is how my request looks in postman
  <img src="https://user-images.githubusercontent.com/54931201/150966369-be70b412-7a33-4772-a5f8-db4a9448a363.png" alt="image" /></p>
  <p>When I try to generate a swagger file. It gives me the following error
  drf_yasg.errors.SwaggerGenerationError: cannot add form parameters when the request has a request body; did you forget to set an appropriate parser class on the view?</p>
  <h2>Minimal Reproduction</h2>
  <pre><code>@swagger_auto_schema(
          operation_id='Create a document',
          operation_description='Create a document by providing file and s3_key',
          manual_parameters=[
              openapi.Parameter('file', openapi.IN_FORM, type=openapi.TYPE_FILE, description='Document to be uploaded'),
              openapi.Parameter('s3_key', openapi.IN_FORM, type=openapi.TYPE_STRING, description='S3 Key of the Document '
                                                                                                 '(folders along with name)')
          ],
          responses={
              status.HTTP_200_OK: openapi.Response(
                  'Success', schema=openapi.Schema(type=openapi.TYPE_OBJECT, properties={
                      'doc_id': openapi.Schema(type=openapi.TYPE_STRING, description='Document ID'),
                      'mime_type': openapi.Schema(type=openapi.TYPE_STRING, description='Mime Type of the Document'),
                      'version_id': openapi.Schema(type=openapi.TYPE_STRING, description='S3 version ID of the document')
                  })
              )
          }
      )
  
  </code></pre>