[BUG][HTML] Vendor-specific media type breaks Example Data

Description

Using a vendor-specific media type causes the Example data section of the operation listing to be empty. Vendor-specific media types are fully supported by OpenAPI Spec 3.0 according to the 'Media Type Names' section on this page: https://swagger.io/docs/specification/media-types/

openapi-generator version

4.0.0-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: Test
  description: Test YAML
  version: '1.0'
servers:
  - url: http://localhost
paths:
  /employees/{id}:
    get:
      operationId: getEmployeeById
      parameters:
        - name: id
          in: path
          required: true
          schema:
            type: string
      responses:
        200:
          description: Success
          content:
            application/vnd.john3300+json;version=1.0:
              schema:
                $ref: '#/components/schemas/employee'
components:
  schemas:
    employee:
      type: object
      properties:
        name:
          type: string
      required:
        - name

Command line used for generation

java -jar openapi-generator-cli-4.0.0-20181217.102953-101.jar generate -g html -i test.yaml

Related issues/PRs

None that I've seen.

Suggest a fix

The code to generate these example sections needs to use a regex to be able to correctly parse these vendor-specific media types and also any additional parameters (e.g. `;version=1.0) that are present.

Start by running the provided Java CLI command with the YAML declaration and inspect the generated HTML operation listing, focusing on the empty Example data section for the vendor-specific media type. Locate the HTML generator code responsible for parsing response content types, then verify that Example data appears for the supplied media type and its version parameter.