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/util/proxyutil/proxyutil.go

@@ -115,8 +115,7 @@ func ApplyUserHeader(sendUserHeader bool, req *http.Request, user identity.Reque
 	}
 
 	namespace, _ := user.GetNamespacedID()
-	switch namespace {
-	case identity.NamespaceUser, identity.NamespaceServiceAccount:
+	if namespace == identity.NamespaceUser || namespace == identity.NamespaceServiceAccount {
 		req.Header.Set(UserHeaderName, user.GetLogin())
 	}
 }