Add backup and restore configuration functionality

V2rayNG/app/src/main/res/values-vi/strings.xml

@@ -175,6 +175,9 @@
     <string name="title_about">About</string>
     <string name="title_source_code">Source code</string>
     <string name="title_tg_channel">Telegram channel</string>
+    <string name="title_configuration_backup">Backup configuration</string>
+    <string name="summary_configuration_backup">Backup storage location: [%s], It will be cleared when the app is uninstalled</string>
+    <string name="title_configuration_restore">Restore configuration</string>
     <string name="title_pref_promotion">Quảng bá server</string>
     <string name="summary_pref_promotion">Quảng cáo, nhấn để biết thêm (Ủng hộ có thể được gỡ bỏ)</string>