[FIX] web: restore notifications about disconnections

The disconnected/connected notifications were broken due to changes in
the way the Notification template was loaded. We need it loaded in
assets as we cannot load it afterward if the server is disconnected.

This was broken by : https://github.com/odoo/odoo/pull/32793



closes odoo/odoo#33252

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>