[FIX] payment: fix portal can click pay when js not loaded

Issue

	- Go to Accounting / Customers / Invoices
	- Pick any invoice not paid
	- Action: Generate a Payment Link
	- Open the link
	- Refresh the page having Javascript disabled
	- Click the Pay Now button

	Traceback

Cause

	If JS is not loaded, the values in the form fields are
	not bound as expected.

	It can also happen with slow connections and fast click
	on the button at the loading. Before the JS is entirely
	loaded (as it is lazy-loaded).

Solution

	Button disabled by default, wait the page to be loaded
	and then activate the button

OPW-2255760

closes odoo/odoo#54128

X-original-commit: 0e7071f2
Signed-off-by: Jason Van Malder (jvm) <jvm@odoo.com>