This makes its api consistent with other add endpoints (see
origin-visit-status-add as one example).
This is preparatory work towards removing origin-visit-upsert.
It's similar to origin-visit-upsert but it does more:
1. it checks for origin consistency
2. it's able to either deal with visit with id (replayer case) and visit with
no id (the existing use case)
Related to T2310