Include NetworkPolicy in chart

It'd be convenient to have NetworkPolicy templates included in the chart for exactly the communication that's needed by the chart, with a `networkPolicy.enabled` value, and some options to configure what pods should be allowed ingress (ingress controller -> api-server/frontend pods).

Start by locating the chart's templates and values files, then review how existing resources and configurable values are defined. Add an optional NetworkPolicy controlled by networkPolicy.enabled, with ingress configuration for the ingress controller to reach the api-server and frontend pods. Done means the policy renders only when enabled and matches the configured communication needs.

Written by the indexing model from the issue text.