Errorneous return type for `findByUserIdAndEntityId` in instance permission repositories

[ahennr]

Currently, UserInstancePermissionRepository and GroupInstancePermissionRepository return an Optional containing a single instance permission.

Optional<UserInstancePermission> findByUserIdAndEntityId(Long userId, Long entityId);
Optional<GroupInstancePermission> findByUserIdAndEntityId(Long userId, Long entityId);

However, a user / group may have multiple permissions for an entity, e.g. READ and UPDATE. So, a list should be returned here.