feat: Setting background synchronization (#3331)

* Changing the background synchronization setting

* add  example

* return function

* style: add clarification note

---------

Co-authored-by: alechkos <93551621+alechkos@users.noreply.github.com>
Co-authored-by: Shir Serlui <70711723+shirser121@users.noreply.github.com>

src/Client.js

@@ -1721,6 +1721,23 @@ class Client extends EventEmitter {
         }, flag);
     }
 
+    /**
+     * Setting background synchronization.
+     * NOTE: this action will take effect after you restart the client.
+     * @param {boolean} flag true/false
+     * @returns {Promise<boolean>}
+     */
+    async setBackgroundSync(flag) {
+        return await this.pupPage.evaluate(async flag => {
+            const backSync = window.Store.Settings.getGlobalOfflineNotifications();
+            if (backSync === flag) {
+                return flag;
+            }
+            await window.Store.Settings.setGlobalOfflineNotifications(flag);
+            return flag;
+        }, flag);
+    }
+    
     /**
      * Get user device count by ID
      * Each WaWeb Connection counts as one device, and the phone (if exists) counts as one