Hello! According to the [docs](https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-mapping-template-reference.html#context-variable-reference) there is an `authorizer` field that is not currently in the `ApiGatewayRequestContext` data type. Is there a reason for this field not being present? If not, then I'd be happy to submit a PR where this field is present in the data type.
