The previous commit allows the sanitizer to be bypassed by some users if
those users are part of one of the `base.group_sanitize_override` group
and if the HTML field is declared as `sanitize_overridable`.
This commit flag frontend HTML fields as `sanitize_overridable`.
See the main commit of this PR for more details.
It also gives the `base.group_sanitize_override` group to the "Editor &
Designer" group.
Part-of: odoo/odoo#97398