[FIX] parter_multi_relation: Reorganize menu hierachy

[u0f]

Before this change, in the Contacts module, the menu items did not follow a consistent hierarchical structure.

Before

After

MT-12511 @moduon @yajo @rafaelbn

[Shide]

I think this should be a PR for Odoo

[u0f]

Odoo PR opened https://github.com/odoo/odoo/pull/234909