A configuration value is needed to be able to control the migration stage of using the cu_private_event_no_actor table in Special:CheckUser.
The Special:CheckUser code will read from the cu_private_event_no_actor table if SCHEMA_COMPAT_READ_NEW is set in the config. The CheckUserInsert service will write to this table if SCHEMA_COMPAT_WRITE_NEW is set in the config.
Acceptance criteria
- Create the CheckUserPrivateEventNoActorMigrationStage configuration value which will be set to SCHEMA_COMPAT_OLD for the time being