Move provisioning proxy steps to the new LSO endpoint

Move away from GÉANT-specific API endpoints in LSO, and instead make use of the generic one

gso/services/provisioning_proxy.py

@@ -88,8 +88,8 @@ _send_delete = partial(_send_request, CUDOperation.DELETE)
 def execute_playbook(
     playbook_name: str,
     callback_route: str,
-    inventory: dict[str, Any],
-    extra_vars: dict[str, Any]
+    inventory: dict[str, Any] | str,
+    extra_vars: dict[str, Any],
 ) -> None:
     """Execute a playbook remotely through the provisioning proxy.
 
@@ -144,7 +144,7 @@ def execute_playbook(
     parameters = {
         "playbook_name": playbook_name,
         "inventory": inventory,
-        "extra_vars": extra_vars
+        "extra_vars": extra_vars,
     }
 
     _send_post("playbook", parameters, callback_route)