[MERGE] website, *: allow adding fonts from Google Fonts

* theme_bootswatch, theme_default, website_theme_install

It is now possible to add very easily a font from Google Fonts under
Customize Theme > Fonts > Add Google Font.

The merge also improves the customize dialog possibilities with a
new 'auto' widget and a 'fontselection' tag.

See sub-commits for details.

task-1974659

closes odoo/odoo#33442

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

Co-authored-by: Andrea Ulliana <aul@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>