Fix empty request name in event log per story #59851134

Implements a `_display_name()` method for Request class so that Event log for Request creations meaningfully identifies Requests. However, this is not a permanent fix, since Request lacks unique identifiers in its attributes.  As temporary measure it makes the display name give the Request's primary key (id) and the `display_name` of the Audit object it is associated with.

Not retroactive to previous database log event entries.