postgresql: improve db.origin_visit_status_add to fix possible replayer issues

In case of an existing OriginVisitStatus entry (typically with the
'created' status), adding a new version of this entry should do an
update instead of ignoring it. This could happen during a replayer session
where the insertion of the OriginVisit used to automatically create an
OriginVisitStatus in "created" status. This would then prevent the
following replayer to actually insert the correct OriginVisitStatus.