✨(back) new endpoint document can_edit

The endpoint can_edit is added to the DocumentViewset, it will give the
information to the frontend application id the current user can edit the
Docs based on the no-websocket rules.

src/backend/core/services/collaboration_services.py

@@ -67,5 +67,5 @@ class CollaborationService:
                 f"Failed to get document connection info. Status code: {response.status_code}, "
                 f"Response: {response.text}"
             )
-
-        return response.json()
+        result = response.json()
+        return result.get("count", 0), result.get("exists", False)