Check whether ongoing notification's priority and importance need to be increased

This blog post describes some "guidelines" for a foreground service's ongoing notification:

https://android-developers.googleblog.com/2018/12/effective-foreground-services-on-android_11.html

There are some guidelines around creating and managing foreground services. For all API levels, a persistent notification with at least PRIORITY_LOW must be shown while the service is created. When targeting API 26+ you will also need to set the notification channel to at least IMPORTANCE_LOW.

Our ongoing notification uses PRIORITY_MIN and the channel uses IMPORTANCE_NONE. Find out whether this affects how the system treats our foreground service, especially on API 26+.

Related to #1146 (closed). Subtask of #1260 (closed).