[FIX] web: image widget is dependent on its record's last_update

As a way to optimize loading, images are not necessarily fetched in db.
They have, in their url a "unique" parameter, which is the last_update date on **the record** and controls on the python-side whether it should get the image from a cache or from the db.

Before this commit, this __last_update field wasn't present in the view, so it wasn't fetched, and writes on a model's image worked but did not refresh.
The image displayed was the old one.

After this commit, when the image field widget is present, we force the loading of the __last_update field of the record.
Upon update, the image displayed is the new one.

OPW 777552

closes #20457