Add has_vinculated_contracts to tree view
CHANGELOG:
### ADDED
- [#921](https://git.coopdevs.org/coopdevs/som-connexio/odoo-somconnexio/-/merge_requests/921) Add has_vinculated_contracts to tree view
Related card: https://trello.com/c/5So05QaQ/1450-t%C3%A9-contractes-vinculats-a-la-vista-tree
Edited by César López Ramírez