code: public Response andContent(Map<String, Object> content) {
          Objects.requireNonNull(content, Required.CONTENT.toString());
          this.content.putAll(content);
  
          return this;
      }
docs: Adds an additional content map to the content rendered in the template.
  Already existing values with the same key are overwritten.
  
  @param content The content map to add
  @return A response object {@link io.mangoo.routing.Response}