Setting unique group key for each notification

prevent_notification_bundling.kt

createNotification() {
  ...
  notificationBuilder.setGroup(getUniqueGroupKey(10))
  ...
}

fun getUniqueGroupKey(sizeOfRandomString: Int): String {
    val random = Random()
    val sb = StringBuilder(sizeOfRandomString)
    for (i in 0 until sizeOfRandomString)
        sb.append(ALLOWED_CHARACTERS[random.nextInt(ALLOWED_CHARACTERS.length)])
    return sb.toString()
}