[MERGE] account/sale(_payment): add invoice and order confirmation and payment in customer portal

This merge improve account and sale customer portal by

 * adding quote confirmation and signature in sale portal;
 * adding a signature widget replacing the one in website_quote;
 * improving the payment form to support URLs and access token
   propagation;
 * adding payment support on orders in sale_payment portal with both
   server2server and form-based payments;
 * adding payment support on invoices in account_payment portal with
   both server2server and form-based payments;
 * globally improving navigation, display and access token use in
   account and sale customer portal;

Please refer to subcommits for more details. Thanks to @jpr-odoo for
preliminary work on those features. Closes #19074.