✨(backend) allow users to mark/unmark documents as favorite

A user can now mark/unmark documents as favorite.
This is done via a new action of the document API endpoint:
/api/v1.0/documents/{document_id}/favorite
POST to mark as favorite / DELETE to unmark

src/backend/core/factories.py

@@ -80,6 +80,13 @@ class DocumentFactory(factory.django.DjangoModelFactory):
             for item in extracted:
                 models.LinkTrace.objects.create(document=self, user=item)
 
+    @factory.post_generation
+    def favorited_by(self, create, extracted, **kwargs):
+        """Mark document as favorited by a list of users."""
+        if create and extracted:
+            for item in extracted:
+                models.DocumentFavorite.objects.create(document=self, user=item)
+
 
 class UserDocumentAccessFactory(factory.django.DjangoModelFactory):
     """Create fake document user accesses for testing."""