Reduce index size: drop superfluous updated_by/at fields

[petli]

A lof of added/updated fields doesn't have to be set:

Work.updated_by should not be set on first creation, it is sufficient with Work.added_by.

Work.updated_at should not be set on first creation, it is sufficient with Work.added_at.

Work.annotations.updated_by should not be set when the annotation is added (or updated) by the same user as Work.added_by.

Work.annotations.updated_at could be skipped if the time is within e.g. 1 minute of Work.added_by. (or shorter?)