[DOC] update upgrade service documentation
[DOC] update upgrade service documentation

 - Update active target versions
 - document `skip_test` endpoint
 - use `requests` in python snippets<Paste>

closes odoo/odoo#31071

Signed-off-by: Christophe Simonis <0e117f2b429bfa19751522a564765b352cb7b946@odoo.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo