Improve workflow Node information logged in the audit

Since NXP-15085, completed and canceled DocumentRoute (Wf instance) and associated RoutingTask are cleaned up (removed) everynight.

But we might want to keep the information about a completed task in the audit on the related document.

We must think aboout what information exactly.

For inatance, we'd like to log when and who completed a given task, and so on.