Feature/refactor validators

Refactor all validators from the deprecated @field_validator pattern that's easily forgettable to apply, into separate annotated types

gso/services/subscriptions.py

@@ -242,7 +242,9 @@ def get_active_site_subscriptions(includes: list[str] | None = None) -> list[Sub
     :return: A list of Subscription objects for sites.
     :rtype: list[Subscription]
     """
-    return get_subscriptions(product_types=["Site"], lifecycles=[SubscriptionLifecycle.ACTIVE], includes=includes)  # type: ignore[list-item]
+    return get_subscriptions(
+        product_types=[ProductType.SITE], lifecycles=[SubscriptionLifecycle.ACTIVE], includes=includes
+    )
 
 
 def get_site_by_name(site_name: str) -> Site: