[FIX] point_of_sale: do not load chat windows on the POS

When the mail_service is started, if there are any running chat sessions,
Chat_windows are created and opened on the point_of_sale frontend.
They also appear in the printed receipt.

To remove them from display we create a new pos_assets_backend template,
which inherits the web.assets_backend and removes the odoobot related assets.

opw 1878185

addons/point_of_sale/views/pos_templates.xml

@@ -1,5 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <odoo>
+<template id="pos_assets_backend" name="POS UI Backend Assets" inherit_id="web.assets_backend" primary="True">
+    <xpath expr="//script[contains(@src, '/mail/static/src/js/services/mail_service.js')]" position="replace"></xpath>
+</template>
+
 <template id="index" name="POS Index">&lt;!DOCTYPE html&gt;
 <html>
     <head>
@@ -31,7 +35,7 @@
         </script>
 
         <t t-call-assets="web.assets_common" t-css="false"/>
-        <t t-call-assets="web.assets_backend" t-css="false"/>
+        <t t-call-assets="point_of_sale.pos_assets_backend" t-css="false"/>
         <t t-call-assets="web_editor.summernote" t-css="false"/>
         <t t-call-assets="web_editor.assets_editor" t-css="false"/>
         <t t-call-assets="point_of_sale.assets"/>