Change primary key for event_identity_registration

[konradkonrad]

From #84:

if a user submits a registration with different event triggers, the second would take precedence over the previous registration -> Change primary key to eon, identity here: https://github.com/shutter-network/rolling-shutter/blob/main/rolling-shutter/keyperimpl/shutterservice/database/sql/migrations/V2_event_based_triggers.sql#L13C18-L13C46 as well as the update on conflict query, also in fired triggers