refactoring - remove not null constraint. When the user is not found in the application, there will be no user_id because the user doesn't exists in the platform

Author: rcsoyer

src/main/resources/db/changelog/user-authentication-event.yml

@@ -28,7 +28,6 @@ databaseChangeLog:
                   constraints:
                     foreignKeyName: fk_user_auth_event_id
                     references: application_user(id)
-                    nullable: false
               - column:
                   name: date_created
                   type: datetime(6)