Fix preshared key not persisted in config (#1474)

* replace the preshared key attribute in LoginRequest protobuff with an optional replacement

* mark old field as deprecated

* fix ui client to also keep preshared key

client/cmd/login.go

@@ -82,12 +82,15 @@ var loginCmd = &cobra.Command{
 
 		loginRequest := proto.LoginRequest{
 			SetupKey:             setupKey,
-			PreSharedKey:         preSharedKey,
 			ManagementUrl:        managementURL,
 			IsLinuxDesktopClient: isLinuxRunningDesktop(),
 			Hostname:             hostName,
 		}
 
+		if rootCmd.PersistentFlags().Changed(preSharedKeyFlag) {
+			loginRequest.OptionalPreSharedKey = &preSharedKey
+		}
+
 		var loginErr error
 
 		var loginResp *proto.LoginResponse