## About the changes
This PR replaces the old systemUser -1 in user-service.ts with the new
SYSTEM_USER -1337 and adds a migration to move events created_by = -1 to
-1337
## Discussion points
Does it make sense to do both of these things? Or should we skip the
migration? How would this behave in a large system with hundreds of
thousands of events, should this be split up?
