[ADD] web_unsplash: Find free high-resolution images from Unsplash

This commit:
1. Adds settings to install the new `web_unsplash` enterprise module.
   See counterpart commit on enterprise for details.
2. Export `ImageWidget` and `update_control_panel` to be able to override them.
3. Add the unsplash access key rights to website designer. (see related OE
   commit)

task-35060
Closes #25825, closes #25637

addons/web_editor/static/src/js/widgets/widgets.js

@@ -1103,6 +1103,7 @@ var MediaDialog = Dialog.extend({
     }),
     custom_events: _.extend({}, Dialog.prototype.custom_events || {}, {
         save_request: '_onSaveRequest',
+        update_control_panel: '_updateControlPanel',
     }),
 
     /**
@@ -1768,5 +1769,6 @@ return {
     MediaDialog: MediaDialog,
     LinkDialog: LinkDialog,
     CropImageDialog: CropImageDialog,
+    ImageWidget: ImageWidget,
 };
 });

addons/web_editor/static/src/xml/editor.xml

@@ -109,7 +109,7 @@
                     <span class="text-muted">— or —</span>
                     <label for="imageurl">Add an image URL</label>
                     <div class="form-group btn-group">
-                        <input type="text" class="form-control url pull-left" id="imageurl" name="url" placeholder="https://www.odoo.com/logo.png" style="width: 320px;"/>
+                        <input type="text" class="form-control url pull-left" id="imageurl" name="url" placeholder="https://www.odoo.com/logo.png" style="width: 250px;"/>
                         <button type="button" class="btn btn-default o_upload_image_url_button" disabled="disabled">Add</button>
                     </div>
                 </div>