jaxrs-jersey generated server stub fails for responses of media type=text/plain

Description

If I generate a jaxrs-jersey server stub from the yaml below, run it and access http://localhost:8080/test/ping it fails with MessageBodyWriter not found for media type=text/plain, type=class io.swagger.api.ApiResponseMessage, genericType=class io.swagger.api.ApiResponseMessage.

Swagger-codegen version

3.0.16

Swagger declaration file content or url

openapi: 3.0.0
info:
  version: '0.0.1'
  title: ''
  description: ''

servers:
  - description: localhost
    url: http://localhost:8080/test
    
paths:
  /ping:
    get:
      responses:
        '200':
          description: OK
          content:
            text/plain:
              schema:
                type: string
                example: pong

Command line used for generation

Steps to reproduce

1. open the attached yaml in https://editor.swagger.io/ and generate jaxrs-jersey server
2. extract and run with mvn clean package jetty:run
3. run the GET /ping from the https://editor.swagger.io/

Related issues/PRs

Suggest a fix/enhancement

Start with the supplied OpenAPI YAML and reproduce the failure by generating the jaxrs-jersey server stub, then running mvn clean package jetty:run and requesting /ping. Inspect the generated server stub's handling of the text/plain response; done means the request completes without a MessageBodyWriter error and returns the declared response.