Ignore repeated ContentType and Accept header generation in specific API code generation

Description

Follow Global Content and Accept Types and only add content/accept types if global types are overridden

Swagger-codegen version

2.4.0

Swagger declaration file content or url

https://github.com/OAI/OpenAPI-Specification/blob/master/examples/v2.0/yaml/petstore.yaml

Yaml Code

    post:
      summary: Create a pet
      operationId: createPets
      tags:
        - pets
      responses:
        "201":
          description: Null response
        default:
          description: unexpected error
          schema:
            $ref: '#/definitions/Error'

Generated Code

public ApiResponse<Object> CreatePets ()
        {

         ...
            // to determine the Content-Type header
            String[] httpContentTypes = new String[] {
                "application/json"
            };
            String httpContentType = this.Configuration.ApiClient.SelectHeaderContentType(httpContentTypes);
            if (httpContentType != null)
                request.SetHeader("Accept", httpContentType);

            // to determine the Accept header
            String[] httpHeaderAccepts = new String[] {
                "application/json"
            };
            String httpHeaderAccept = this.Configuration.ApiClient.SelectHeaderAccept(httpHeaderAccepts);
            if (httpHeaderAccept != null)
                request.SetHeader("Accept", httpHeaderAccept);

...
        }

Command line used for generation

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate
-i https://raw.githubusercontent.com/OAI/OpenAPI-Specification/master/examples/v2.0/yaml/petstore.yaml
-l csharp
-o ./tmp/DefaultGeneration \

Steps to reproduce

Just generare with csharp as language

Suggest a fix/enhancement

Please consider only if the content types are overriden in specific API. Else, there is lot of code that is getting bloated which isn't required. As there will be a global Accept/Content-type's defined, it can be ignored in each api code generation. If there is specific data defined with in api, it can be generated.
Please consider it similar to authMethods tag in DefaultGenerator.java

Start with DefaultGenerator.java and the csharp generation path, using the petstore.yaml example and the reported generated CreatePets method as the reference case. Check how global and operation-level content and Accept types are represented, then verify that generation omits repeated per-operation header code unless an operation overrides the global types.