Updated NotificationHelper to use highest notification priority (PRIORITY_MAX) (#203)

We should ensure that notifications always have the highest priority also on older devices.

Co-authored-by: Johannes Münichsdorfer <johannes.muenichsdorfer@tum.de>
Co-authored-by: Jakob Möller <jakob.moeller@sap.com>
Co-authored-by: Hee Tatt Ooi <hee.tatt.ooi@sap.com>

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/notification/NotificationHelper.kt

@@ -92,7 +92,7 @@ object NotificationHelper {
     private fun buildNotification(title: String, content: String, visibility: Int): Notification? {
         val builder = NotificationCompat.Builder(CoronaWarnApplication.getAppContext(), channelId)
             .setSmallIcon(NotificationConstants.NOTIFICATION_SMALL_ICON)
-            .setPriority(NotificationCompat.PRIORITY_HIGH)
+            .setPriority(NotificationCompat.PRIORITY_MAX)
             .setVisibility(visibility)
             .setContentIntent(createPendingIntentToMainActivity())
             .setAutoCancel(true)