[FIX] portal: show line return in chatter message
[FIX] portal: show line return in chatter message

In the frontend only plaintext is saved without any javascript fiddling
so in the controller it should be adapted to be saved.

With this change, the behavior is more similar to backend chatter which
sends html (processed by javascript) to the server.

opw-1817918
closes #23706

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo