[BUG][JAVA] Content type of response seems to be ignored and always set to application/json

Created by: TimFaehrtBahn

Description

The defined content type within the open api spec seems to be ignored. The generated code always contains "application/json".

openapi-generator version

openapi-generator-cli-4.3.1.jar

OpenAPI declaration file content or url

[...]
 "200": {
            "description": "Success",
            "headers": {
              "Cache-Control": {
                "description": "Controls whether and how long response can be cached by consumers, defaults to 'no-cache, no-store'.",
                "style": "simple",
                "schema": {
                  "type": "string"
                }
              }
            },
            "content": {
              "application/vnd.de.db.ris+json": {
                "schema": {
                  "$ref": "#/components/schemas/BoardPublicArrival"
                }
              }
            }
          }
[...]

##### Command line used for generation

java -jar openapi-generator-cli-4.3.1.jar generate -g java -i swagger.yml --library native --api-package innoapi.api --invoker-package innoapi.invoker --model-package innoapi.model

##### Steps to reproduce
Look in the code and the accept header.
`
localVarRequestBuilder.header("Accept", "application/json");
`

##### Related issues/PRs
/

##### Suggest a fix
Content type has to evaulated for setting the accept header.