Swift notification plugin (#436)

* Add Swift notification plugin

* Hash the metadata

* Validate min sendable amount

* Remove initializer as base class, UNNotificationServiceExtension, has no default initializer

* Set the PaymentMethod

* Handle PaymentDetails in SwapUpdated

* Improve payment text

lib/bindings/langs/swift/Sources/BreezSDKLiquid/TaskProtocol.swift

@@ -0,0 +1,33 @@
+import UserNotifications
+
+public protocol TaskProtocol : EventListener {
+    var payload: String { get set }
+    var contentHandler: ((UNNotificationContent) -> Void)? { get set }
+    var bestAttemptContent: UNMutableNotificationContent? { get set }
+    
+    func start(liquidSDK: BindingLiquidSdk) throws
+    func onShutdown()
+}
+
+extension TaskProtocol {
+    func displayPushNotification(title: String, body: String? = nil, logger: ServiceLogger, threadIdentifier: String? = nil) {
+        logger.log(tag: "TaskProtocol", line:"displayPushNotification \(title)", level: "INFO")
+        guard
+            let contentHandler = contentHandler,
+            let bestAttemptContent = bestAttemptContent
+        else {
+            return
+        }
+        
+        if let body = body {
+            bestAttemptContent.body = body
+        }
+
+        if let threadIdentifier = threadIdentifier {
+            bestAttemptContent.threadIdentifier = threadIdentifier
+        }
+        
+        bestAttemptContent.title = title
+        contentHandler(bestAttemptContent)
+    }
+}