docs: def _get_headers(self, route: str, annotation: ResourceAnnotation) -> Dict:
          """Gets headers for the provided route.
  
          :param route: The route to get example values for.
          :type route: werkzeug.routing.Rule for a flask api.
          :param annotation: Schema annotation for the method to be requested.
          :type annotation: doctor.resource.ResourceAnnotation
          :retruns: A dict containing headers.
          """
          headers = self.headers.copy()
          defined_header_values = self.defined_header_values.get(
              (annotation.http_method.lower(), str(route)))
          if defined_header_values is not None:
              if defined_header_values['update']:
                  headers.update(defined_header_values['values'])
              else:
                  headers = defined_header_values['values']
          return headers