when "test quota on write" fails, it should notify pod owner

In catching up on a lot of discussion and updates, it seems that when the "test quota on write" fails it results in a notification to the attempting writer -- so if @kjetilk tries to write to @RubenVerborgh's INBOX and that write would exhaust quota, @kjetilk gets notified -- but @RubenVerborgh does not.

This is troublesome, as @kjetilk's best (and possibly only) way to inform @RubenVerborgh of this problem is via his inbox ... which is full. I think that this is a place where NSS might use @RubenVerborgh's email address to send such a notification without consuming further NSS-quota.

Originally posted in https://github.com/solid/node-solid-server/issues/918#issuecomment-450062727

Beginne damit, die Node.js-Implementierung des Fehlers „test quota on write“ und den Benachrichtigungspfad zu finden, und lies anschließend zur Einordnung die Diskussion im verlinkten Issue 918. Die Arbeit ist abgeschlossen, wenn der Pod-Owner über den Quota-Fehler benachrichtigt wird, ohne zusätzliche Quota zu verbrauchen, während das bestehende Benachrichtigungsverhalten für Writer weiterhin verstanden und abgedeckt ist.