[FIX] web, website: fix font path for bootstrap

Before this commit, if you or a lib uses Glyphicons, the font was loaded from
/web/content/fonts/ (or /web/static/src/less/fonts/ in debug=assets)

It is because bootstrap is imported from /web/static/src/less/import_boostrap.less
not directly from /web/static/lib/bootstrap/less/bootstrap.less

Now, we use absolute path to load font, overriding the variable define in
variables.less from bootstrap.

addons/web/static/src/less/bootstrap_overridden.less

@@ -101,3 +101,5 @@
         overflow-x: initial;
     }
 }
+
+@icon-font-path: "/web/static/lib/bootstrap/fonts/";

addons/website/static/src/less/website.ui.less

@@ -51,3 +51,5 @@ body.o_connected_user {
         }
     }
 }
+
+@icon-font-path: "/web/static/lib/bootstrap/fonts/";