getOrCreateNotificationChannelId

Returns the channel id for a valid NotificationChannel, creating one if necessary.

First, if Constants.BRAZE_PUSH_NOTIFICATION_CHANNEL_ID_KEY key is present in notificationExtras's and is the id of a valid NotificationChannel, this id will be returned.

Next, if the channel with id Constants.BRAZE_PUSH_DEFAULT_NOTIFICATION_CHANNEL_ID exists, then Constants.BRAZE_PUSH_DEFAULT_NOTIFICATION_CHANNEL_ID will be returned.

Finally, if neither of the cases above is true, a channel with id Constants.BRAZE_PUSH_DEFAULT_NOTIFICATION_CHANNEL_ID will be created and Constants.BRAZE_PUSH_DEFAULT_NOTIFICATION_CHANNEL_ID will be returned.