✨(backend) add soft delete to documents and refactor db queryset

Now that we have introduced a document tree structure, it is not
possible to allow deleting documents anymore as it impacts the whole
subtree below the deleted document and the consequences are too big.

We introduce soft delete in order to give a second thought to the
document's owner (who is the only one to be allowed to delete a
document). After a document is soft deleted, the owner can still
see it in the trashbin (/api/v1.0/documents/trashbin).
After a grace period (30 days be default) the document disappears
from the trashbin and can't be restored anymore. Note that even
then it is still kept in database. Cleaning the database to erase
deleted documents after the grace period can be done as a maintenance
script.

src/backend/core/factories.py

@@ -77,6 +77,7 @@ class DocumentFactory(factory.django.DjangoModelFactory):
     excerpt = factory.Sequence(lambda n: f"excerpt{n}")
     content = factory.Sequence(lambda n: f"content{n}")
     creator = factory.SubFactory(UserFactory)
+    deleted_at = None
     link_reach = factory.fuzzy.FuzzyChoice(
         [a[0] for a in models.LinkReachChoices.choices]
     )
@@ -94,11 +95,19 @@ class DocumentFactory(factory.django.DjangoModelFactory):
 
         if parent:
             # Add as a child node
+            kwargs["ancestors_deleted_at"] = (
+                kwargs.get("ancestors_deleted_at") or parent.ancestors_deleted_at
+            )
             return parent.add_child(instance=model_class(**kwargs))
 
         # Add as a root node
         return model_class.add_root(instance=model_class(**kwargs))
 
+    @factory.lazy_attribute
+    def ancestors_deleted_at(self):
+        """Should always be set when "deleted_at" is set."""
+        return self.deleted_at
+
     @factory.post_generation
     def users(self, create, extracted, **kwargs):
         """Add users to document from a given list of users with or without roles."""
@@ -109,6 +118,16 @@ class DocumentFactory(factory.django.DjangoModelFactory):
                 else:
                     UserDocumentAccessFactory(document=self, user=item[0], role=item[1])
 
+    @factory.post_generation
+    def teams(self, create, extracted, **kwargs):
+        """Add teams to document from a given list of teams with or without roles."""
+        if create and extracted:
+            for item in extracted:
+                if isinstance(item, str):
+                    TeamDocumentAccessFactory(document=self, team=item)
+                else:
+                    TeamDocumentAccessFactory(document=self, team=item[0], role=item[1])
+
     @factory.post_generation
     def link_traces(self, create, extracted, **kwargs):
         """Add link traces to document from a given list of users."""