[BugBash][CLI]better report error if PrivateEndpoint connection specified while updating network rule

[juniwang]

Is your feature request related to a problem? Please describe.

better report error if PrivateEndpoint connection specified while updating network rule.

Describe the solution you'd like

Try command az webpubsub network-rule update -g jw1111 -n jw2222 --connection-name --allow ClientConnection Trace. Notify that the --connection-name is empty. So nothing gets updated. Suggest show a friendly warning message that a connection is required.

Additional context

Add any other context or screenshots about the feature request here.

[zackliu]

https://github.com/Azure/azure-cli-extensions/pull/4049