[IMP] website: allow to add items in table of content

The goal of this commit is to add the "Add Item" option
for 'table of content' to be able to add new items.

Part of https://github.com/odoo/odoo/pull/68061
task-2431484

addons/website/views/snippets/s_table_of_content.xml

@@ -47,6 +47,15 @@
 </template>
 
 <template id="s_table_of_content_options" inherit_id="website.snippet_options">
+    <xpath expr="//t[@t-call='web_editor.snippet_options_background_options']" position="before">
+        <div data-js="MultipleItems" data-selector=".s_table_of_content">
+            <we-row string="Content">
+                <we-button data-add-item="" data-item=".s_table_of_content_main > section:last" data-select-item="" data-no-preview="true" class="o_we_bg_brand_primary">
+                    Add Item
+                </we-button>
+            </we-row>
+        </div>
+    </xpath>
     <xpath expr="." position="inside">
         <div data-js="TableOfContent" data-selector=".s_table_of_content"/>
         <div data-js="TableOfContentNavbar" data-selector=".s_table_of_content_navbar_wrap">