Add minimal auditing to record entry

[blootsvoets]

There should be some log or statement of which user uploaded or processed an entry. Auditing could be added to a record.audit field, with an array of status changes, time and users involved. Entries could have the form of {userId?, clientId?, time?, operation: CREATE | READ | UPDATE | DELETE, entityType: record | contents | metadata, recordId?, fileName?, status: INCOMPLETE | READY |...}

A simpler implementation could be to just list a createdBy field in record.metadata with type {userId?: <userId>, clientId?: <clientId>}.

In the former case, the API should probably also be extended.

@nivemaham what do you think?