Add the file location to the event metrics

[imsdu]

Motivation
We have currently no way to determine if a physical file is an orphan, that is to say it has not been registered in Nexus.
With the new ways to register files (delegation, presigned urls), where the client plays a most important role, this is most likely to happen.

Storing files in S3 having a cost, identifying those orphans will be useful.
Adding the location in the fields in event metrics will allow to use it as a reverse index and find if any file event is associated with this location.

Not in scope

1. The tool allowing to identify orphans will be part of another ticket
2. An endpoint to find the Nexus files from the location