[FIX] website_sale: Added base_url to schema.org microdata tags

Steps to reproduce the bug:
- install eCommerce module with assets
- go to any product page
- check the source code with https://validator.schema.org/

Notice that the 'image' and 'url' microdata tags have no base url,
so the engine assumes http://schema.org/

 to be the base url. This
makes certain ad trackers such as facebook pixel unable to detect
the product being sold.

This commit adds the base_url field to both tags so that they are
correctly traced.

opw-2830058

closes odoo/odoo#97215

Signed-off-by: William Braeckman (wbr) <wbr@odoo.com>