[IMP] maintenance: restrict deletion of equipment if requests exists
[IMP] maintenance: restrict deletion of equipment if requests exists

Loosing data about existing requests is not good idea when managing
maintenance. It is better to ensure there are no ongoing requests
and prevent deletion if it is the case.

Closes #18794 .

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo