[IMP] website_portal: increase default items per page to 20
[IMP] website_portal: increase default items per page to 20

Feedback: 10 is very few

ygol/odoo,hip-odoo/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,hip-odoo/odoo,hip-odoo/odoo,hip-odoo/odoo,ygol/odoo,dfang/odoo,dfang/odoo,ygol/odoo,ygol/odoo,ygol/odoo,dfang/odoo,dfang/odoo,dfang/odoo,hip-odoo/odoo,ygol/odoo