feat: Handle iOS background downloads

ios/App/App/AppDelegate.swift

@@ -6,6 +6,7 @@ import RealmSwift
 class AppDelegate: UIResponder, UIApplicationDelegate {
 
     var window: UIWindow?
+    var backgroundCompletionHandler: (() -> Void)?
     
     func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
         // Override point for customization after application launch.
@@ -72,6 +73,12 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         // tracking app url opens, make sure to keep this call
         return ApplicationDelegateProxy.shared.application(application, continue: userActivity, restorationHandler: restorationHandler)
     }
+    
+    func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
+        // Stores the completion handler for background downloads
+        // The identifier of this method can be ignored at this time as we only have one background url session
+        backgroundCompletionHandler = completionHandler
+    }
 
     override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
         super.touchesBegan(touches, with: event)