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>

index.d.ts

@@ -180,6 +180,13 @@ declare namespace WAWebJS {
          */
         setAutoDownloadVideos(flag: boolean): Promise<void>
 
+        /**
+         * Changing the background synchronization setting.
+         * NOTE: this action will take effect after you restart the client.
+         * @param flag true/false on or off
+         */
+        setBackgroundSync(flag: boolean): Promise<void>
+
         /**
          * Get user device count by ID
          * Each WaWeb Connection counts as one device, and the phone (if exists) counts as one