added const string getqr and statusqr

lib/shared/preference_constant.dart

 // ignore_for_file: unnecessary_nullable_for_final_variable_declarations
 
 const kUrlDolan = "url_dolan";
+const kUrlGetQr = "url_get_qr";
+const kUrlStatusQr = "url_status_qr";
 const kUrlCloseLoop = "url_close_loop";
 const kMerchantName = "merchant_name";
 const kUserName = "user_name";