Update Tutorial to Remove Backend Plugin

[IfSentient]

Our general usage pattern for app platform apps has moved in the direction preference to direct API server access, without routing traffic through a backend plugin, excepting the need for additional routes (until aggregated API servers become available). The tutorial should be updated to remove the backend plugin components, and local setup should be able to handle the UI talking directly to the API server.

The tutorial should be expanded to cover admission/mutation webhooks in the operator for admission control as well, as that was something previously offloaded to the backend plugin.