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_test.go

@@ -203,7 +203,7 @@ func TestProxy_Hook(t *testing.T) {
 	}
 	cache := &fakeCache{data: make(map[string][]byte)}
 	userId := int64(1)
-	userID := authn.MustNewNamespaceID(authn.NamespaceUser, userId)
+	userID := authn.NewNamespaceID(authn.NamespaceUser, userId)
 
 	// withRole creates a test case for a user with a specific role.
 	withRole := func(role string) func(t *testing.T) {