[FIX] website_forum: fix spacing issues

This commit aims to fix an issue on forum posts, about comments being
placed directly next to each other without having a gap between them,
making it harder to visually recognize items at first glance.

To handle this issue, we simply add a `d-flex gap-x` utility classes
to ensure these elements receive some spacing between them.

closes odoo/odoo#155364

Signed-off-by: Julien Castiaux (juc) <juc@odoo.com>

addons/website_forum/views/forum_forum_templates_post.xml

@@ -506,7 +506,7 @@
 
 <!-- Utility template: Post a Comment -->
 <template id="post_comment">
-    <div class="o_wforum_post_comments_container rounded">
+    <div class="o_wforum_post_comments_container d-flex flex-column gap-2 rounded">
         <div class="css_editable_mode_hidden o_wforum_readable">
             <form t-att-id="_collapse_uid" class="oe_comment_grey js_website_submit_form js_wforum_submit_form collapse rounded o_cc2 p-2"
                 t-attf-action="/forum/#{slug(forum)}/post/#{slug(object)}/comment" method="POST">