onRequest method
Called when the request is about to be sent.
Implementation
@override
void onRequest(RequestOptions options, RequestInterceptorHandler handler) {
// Add the timezone and request timestamp headers
options.headers["X-Timezone"] = _getTimezoneOffset();
options.headers["X-Requested-At"] =
DateTime.now().toIso8601StringWithOffset();
// Continue the request chain
handler.next(options);
}