[FIX] web_editor: remove the possibility to edit readonly image field

Steps to reproduce the bug:
- Add multiple images on a product page
- Go to the shop and edit an image of this product by double clicking
on a small image on the carousel thumbnail
- Save
-> Nothing happens and the image is not updated

The goal of this commit is to ensure that a field of type image is not
`readonly` before adding the `contenteditable` attribute to its image.

task-3122670

closes odoo#114587

X-original-commit: 36fb765
Signed-off-by: Benoit Socias (bso) <bso@odoo.com>

Author: loco-odoo

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -286,7 +286,7 @@ const Wysiwyg = Widget.extend({
                     }
                     if ($field.data('oe-type') === "image") {
                         $field.attr('contenteditable', false);
-                        $field.find('img').attr('contenteditable', true);
+                        $field.find('img').attr('contenteditable', $field.data('oe-readonly') !== 1);
                     }
                     if ($field.is('[data-oe-many2one-id]')) {
                         $field.attr('contenteditable', false);