[FIX] portal, sale: scroll correctly if fixed header

Depending of the configuration, on the portal, anchor do not consider the
header, so a part of the text is hidden by the navbar.

task-2290213

closes odoo/odoo#60415

X-original-commit: 2cd9a9d12f4cd7352430c166145a7488af0c120c
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>
Signed-off-by: Romain Derie <rdeodoo@users.noreply.github.com>

addons/portal/views/portal_templates.xml

@@ -532,7 +532,7 @@
             :pid : identifier of the partner signing the token
     -->
     <template id="message_thread">
-        <div id="discussion" class="d-print-none o_portal_chatter o_not_editable p-0"
+        <div id="discussion" data-anchor="true" class="d-print-none o_portal_chatter o_not_editable p-0"
             t-att-data-token="token" t-att-data-res_model="object._name" t-att-data-pid="pid" t-att-data-hash="hash" t-att-data-res_id="object.id" t-att-data-pager_step="message_per_page or 10" t-att-data-allow_composer="'0' if disable_composer else '1'">
         </div>
     </template>

addons/sale/static/src/js/sale_portal_sidebar.js

@@ -88,7 +88,9 @@ publicWidget.registry.SalePortalSidebar = PortalSidebar.extend({
                     }
                     break;
             }
+            el.setAttribute('data-anchor', true);
         });
+        this.trigger_up('widgets_start_request', {$target: $bsSidenav});
     },
     /**
      * extract text of menu title for sidebar