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/contexthandler/contexthandler_test.go

@@ -44,7 +44,7 @@ func TestContextHandler(t *testing.T) {
 	})
 
 	t.Run("should set identity on successful authentication", func(t *testing.T) {
-		identity := &authn.Identity{ID: authn.MustNewNamespaceID(authn.NamespaceUser, 1), OrgID: 1}
+		identity := &authn.Identity{ID: authn.NewNamespaceID(authn.NamespaceUser, 1), OrgID: 1}
 		handler := contexthandler.ProvideService(
 			setting.NewCfg(),
 			tracing.InitializeTracerForTest(),