Chore: Fix error handling in postDashboard, remove UserDisplayDTO, fix live redis client initialization (#87206)

* clean up error handling in postDashboard and remove UserDisplayDTO

* replace GetUserUID with GetUID and GetNamespacedUID, enforce namespace constant type

* lint fix

* lint fix

* more lint fixes

pkg/services/authn/authnimpl/service.go

@@ -373,7 +373,7 @@ func (s *Service) resolveIdenity(ctx context.Context, orgID int64, namespaceID a
 			}}, nil
 	}
 
-	resolver, ok := s.idenityResolverClients[namespaceID.Namespace()]
+	resolver, ok := s.idenityResolverClients[namespaceID.Namespace().String()]
 	if !ok {
 		return nil, authn.ErrUnsupportedIdentity.Errorf("no resolver for : %s", namespaceID.Namespace())
 	}

pkg/services/authn/authnimpl/service_test.go

@@ -514,7 +514,7 @@ func TestService_ResolveIdentity(t *testing.T) {
 	t.Run("should resolve for valid namespace if client is registered", func(t *testing.T) {
 		svc := setupTests(t, func(svc *Service) {
 			svc.RegisterClient(&authntest.MockClient{
-				NamespaceFunc: func() string { return authn.NamespaceAPIKey },
+				NamespaceFunc: func() string { return authn.NamespaceAPIKey.String() },
 				ResolveIdentityFunc: func(ctx context.Context, orgID int64, namespaceID authn.NamespaceID) (*authn.Identity, error) {
 					return &authn.Identity{}, nil
 				},