[REF] website: make the google font "Roboto" the default website font

Before this commit, the default font for the website was the bootstrap
one, which is a series of many fonts which should at least contain one
which is present on every user system.

The problem is that commit https://github.com/odoo/odoo/commit/ed18095127b20da516fa5ada943b2dd6d5c84652
added the definition of a Roboto font, available in all assets... and
Roboto is part of the bootstrap font. This added a new font loading on
page load and that loading is not optimized at the moment. This thus
broke our work to improve google pagespeed ratings.

This commit replaces the bootstrap font with a forced Roboto font whose
loading is handled by an optimized loading of the related google font.
This also improves the very default font of the website by making it
more stable accross different browser (we will always use the loaded
Roboto font instead of relying on the user system fonts).

Part of https://github.com/odoo/odoo/pull/37293

addons/website/static/src/scss/primary_variables.scss

@@ -69,7 +69,7 @@ $o-user-website-values: () !default;
 //------------------------------------------------------------------------------
 
 $o-theme-fonts: (
-    (-apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Noto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji"), // This is BS default
+    ('Roboto', Noto, sans-serif),
     ('Open Sans', sans-serif),
     ('Source Sans Pro', sans-serif),
     ('Raleway', sans-serif),
@@ -77,7 +77,7 @@ $o-theme-fonts: (
     ('Arvo', Times, serif),
 ) !default;
 $o-theme-font-urls: (
-    null,
+    'Roboto:400,400i,700,700i',
     'Open+Sans:400,400i,700,700i',
     'Source+Sans+Pro:400,400i,700,700i',
     'Raleway:400,400i,700,700i',
@@ -85,7 +85,7 @@ $o-theme-font-urls: (
     'Arvo:400,400i,700,700i',
 ) !default;
 $o-theme-font-names: (
-    'Bootstrap',
+    'Roboto',
     'Open Sans',
     'Source Sans Pro',
     'Raleway',