[FIX] account: add a block at the bottom of the invoice report

It is not possible to add a block at the bottom of the invoice report
with Studio

Steps to reproduce:
1. Install Invoicing and Studio
2. Open Invoicing, toggle Studio and open Reports
3. Open the Invoice report
4. Try to add a text block after the payment terms, Studio doesn't let
   you

Solution:
Put all the content of the invoice in the page div

opw-3443086

closes odoo/odoo#134651

Signed-off-by: William André (wan) <wan@odoo.com>