*: mail, website_livechat

This commit adds new option in Livechat Button visibility
"Show with notifcation", which allow to see livechat button
and also display a customizable floating text next to button.

This text appears 1 second after the livechat button become visible.

Task-2937993

closes odoo/odoo#100689

Signed-off-by: Louis Wicket (wil) <wil@odoo.com>