In a ManyToMany relationship, doctrine does take care only of the owning
side of a relationship to inspect changes.
([see
documentation](https://www.doctrine-project.org/projects/doctrine-orm/en/current/reference/unitofwork-associations.html#important-concepts))
This commit mark as "internal" the methods add/removeSocialAction on the
inversed side (`Evaluation`) and let the methods add/removeEvaluation
on the owning side (`SocialAction`) update the inversed side.
The usage is also adapted into SocialWorkMetadata's importer.
