Embedding a video can't work because it embeds an iframe, which is not supported
by most email clients for security reasons.
(What happens when Gmail shows embedded videos in displayed emails, is that you
send a link in the email body, and it is at rendering that Gmail adds the iframe
into the page.)
In true bugfix fashion, we hide the button.
When the "res_model" is "mail.compose.message", we generate a widget with the
noVideo option.
Essentially a foward-port of v11 commit: 264f89f63f
opw 1905497
closesodoo/odoo#28912
len-odoo
a48a4b1c0b