[FIX] website_sale: missing image on ecommerce product metadata

Before this commit:
No "image" metadata was available for products on the ecommerce main page (/shop). As such search engines SEO will be less effective.
In the case of the client, using "Google Search Console" would give the message: `Missing field 'image'` as a "Top Warning"

Note:
This issue was introduced by:
https://github.com/odoo/odoo/pull/30656
and was partially solved by:
https://github.com/odoo/odoo/pull/37870/commits/c66892e65d2ae0ca31a686f65d4b517a9d7ffd0b



OPW-2509546

closes odoo/odoo#74880

Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>