Cannot use the /docs to verify API

#9786 ### Description

I am starting to use the swagger-codegen. I build and try to run the PetStore nodejs server sample.
The server is started correctly at HTTP://localhost:8080/. Anyway when I try to verify APi, there are two issues:

1. On HTTP://localhost:8080/docs, choose one API, eg, /pet/1/uploadImage, it actually cannot specify anything for body. Similar to other API, you cannot specify the body also.
2. When the requestBody is "multipart/form-data", even though I try to use other API testing tool(Eg, postman) to specify the body of API /pet/1/uploadImage, only "additionalMetadata" get all body input, while "file" and "petId" is empty for the controller method. Should the controller only has one parameter for whole body?

Swagger-codegen version

I am using latest code of branch 3.0.0.

Swagger declaration file content or url

I did not make a line of code change for the testing.

Command line used for generation

Steps to reproduce

1. git clone -b 3.0.0 https://github.com/swagger-api/swagger-codegen
2. cd swagger-codegen/samples/server/petstore/nodejs
3. npm install
4. npm start
5. HTTP://localhost:8080/docs
6. go to /pet/{id}/uploadImage API and cannot find way to specify body parameters.
7. use postman to specify body parameters for same API, but controller does not accept multi body parameters.

Related issues/PRs

Suggest a fix/enhancement

Reproduce the problem from samples/server/petstore/nodejs by running npm install and npm start, then open the generated /docs entry for /pet/{id}/uploadImage. Inspect the generated controller handling that operation and compare its multipart/form-data behavior with the request sent from Postman. Done means the docs expose the body inputs and the controller receives file, petId, and additionalMetadata correctly.