feature: add support for custom response Content-Types (problem+json, etc.)

[maks-oleksyuk]

Overview

This PR enhances OpenAPI response generation by adding support for custom Content-Types.
Now responses can correctly specify and document schemas for:

• application/problem+json (RFC 7807 error format)
• application/vnd.api+json (JSON:API)
• application/octet-stream (binary data)
• text/plain (plain text)
• Defaulting to application/json when no content-type is provided

Example

return new JsonResponse([
    'type' => 'https://example.com/probs/invalid-user-id',
    'title' => 'Invalid user ID',
    'status' => 404,
    'detail' => 'User with given ID not found',
], 404, ['Content-Type' => 'application/problem+json']);

Generated OpenAPI

404:
  description: Invalid user ID
  content:
    application/problem+json:
      schema:
        type: object
        properties:
          type: { type: string, example: https://example.com/probs/invalid-user-id }
          title: { type: string, example: Invalid user ID }
          status: { type: integer, example: 404 }
          detail: { type: string, example: User with given ID not found }

Tests

Added unit tests for JSON, problem+json, text/plain, binary, nullable, and arrays.