This commit splits the old `NodeAPIEndpoint` type into three;

* `NodeAPIEndpoint`, which will also contain the freeze endpoint;
* `AnnuaireAPIEndpoint`, which is the plain old node API without extra
  features;
* `CorpusAPIEndpoint`, which will also contain the publishin endpoint.

This split ensures that we don't add endpoints which do not belong to
all three categories, like before.