fix: User checks (#139)

* check uniqueness on create and register user

* change user email, reserve release unique email

* usergrant unique aggregate

* usergrant uniqueness

* validate UserGrant

* fix tests

internal/eventstore/eventstore.go

@@ -41,7 +41,6 @@ func (es *eventstore) PushAggregates(ctx context.Context, aggregates ...*models.
 	if err != nil {
 		return err
 	}
-
 	return nil
 }