✨(backend) add creator field on document and allow filtering on it

We want to be able to limit the documents displayed on a logged-in user's
list view by the documents they created or by the documents that other
users created.

This is different from having the "owner" role on a document because this
can be acquired and even lost. What we want here is to be able to
identify documents by the user who created them so we add a new field.

src/backend/core/models.py

@@ -341,6 +341,9 @@ class Document(BaseModel):
     link_role = models.CharField(
         max_length=20, choices=LinkRoleChoices.choices, default=LinkRoleChoices.READER
     )
+    creator = models.ForeignKey(
+        User, on_delete=models.RESTRICT, related_name="documents_created"
+    )
 
     _content = None