Identity: Use typed version of namespace id (#87257)

* Remove different constructors and only use NewNamespaceID

* AdminUser: check typed namespace id

* Identity: Add convinient function to parse valid user id when type is either user or service account

* Annotations: Use typed namespace id instead

pkg/services/authn/clients/proxy.go

@@ -124,7 +124,7 @@ func (c *Proxy) retrieveIDFromCache(ctx context.Context, cacheKey string, r *aut
 	}
 
 	return &authn.Identity{
-		ID:    authn.NewNamespaceIDUnchecked(authn.NamespaceUser, uid),
+		ID:    authn.NewNamespaceID(authn.NamespaceUser, uid),
 		OrgID: r.OrgID,
 		// FIXME: This does not match the actual auth module used, but should not have any impact
 		// Maybe caching the auth module used with the user ID would be a good idea