add setting for syncing only over wifi

Issue: #541

Author: AlphaGergedan

Diff for: lib/data/prefs.dart

@@ -62,6 +62,7 @@ abstract class Prefs {
 
   static late final PlainPref<Uint8List?> pfp;
   static late final PlainPref<bool> syncInBackground;
+  static late final PlainPref<bool> onlySyncOverWifi;
 
   static late final PlainPref<ThemeMode> appTheme;
 
@@ -168,6 +169,7 @@ abstract class Prefs {
 
     pfp = PlainPref('pfp', null);
     syncInBackground = PlainPref('syncInBackground', true);
+    onlySyncOverWifi = PlainPref('onlySyncOverWifi', true);
 
     appTheme = PlainPref('appTheme', ThemeMode.system);
     platform = PlainPref('platform', defaultTargetPlatform);

Diff for: lib/pages/home/settings.dart

@@ -329,6 +329,15 @@ class _SettingsPageState extends State<SettingsPage> {
                 },
                 pref: Prefs.hyperlegibleFont,
               ),
+              SettingsSwitch(
+                title: 'Sync notes only over WiFi',
+                subtitle: 'If disabled mobile data may be used to sync notes',
+                iconBuilder: (i) => switch (Prefs.platform.value) {
+                  TargetPlatform.iOS || TargetPlatform.macOS => Icons.wifi_rounded,
+                  _ => Icons.wifi_sharp,
+                },
+                pref: Prefs.onlySyncOverWifi,
+              ),
               SettingsSubtitle(subtitle: t.settings.prefCategories.writing),
               SettingsSwitch(
                 title: t.settings.prefLabels.preferGreyscale,