Always attempt automatic backup creation

- Defaults to every 12 hours
- Minimum number of backups is now 2, just to offer some level of redundancy in case something happens
- If it's missing storage permissions, it'll fail but that's the user's loss if they somehow haven't granted that permission yet

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferencesHelper.kt

@@ -214,7 +214,7 @@ class PreferencesHelper(val context: Context) {
 
     fun numberOfBackups() = flowPrefs.getInt("backup_slots", 2)
 
-    fun backupInterval() = flowPrefs.getInt("backup_interval", 0)
+    fun backupInterval() = flowPrefs.getInt("backup_interval", 12)
 
     fun removeAfterReadSlots() = prefs.getInt(Keys.removeAfterReadSlots, -1)