enh: validate user id before saving group

backend/open_webui/models/groups.py

@@ -85,7 +85,6 @@ class GroupForm(BaseModel):
 
 class GroupUpdateForm(GroupForm):
     user_ids: Optional[list[str]] = None
-    admin_ids: Optional[list[str]] = None
 
 
 class GroupTable:

backend/open_webui/models/users.py

@@ -300,5 +300,10 @@ class UsersTable:
         except Exception:
             return None
 
+    def get_valid_user_ids(self, user_ids: list[str]) -> list[str]:
+        with get_db() as db:
+            users = db.query(User).filter(User.id.in_(user_ids)).all()
+            return [user.id for user in users]
+
 
 Users = UsersTable()