Leverage deprecated features subsystem and feature flags

[Zerpet]

Is your feature request related to a problem?

RabbitMQ upgrades require certain number of feature flags to be enabled. Specially in the upgrade from 3.13.x to 4.0.x, we require all stable feature flags enabled, and khepri 3.13 disabled. This information is visible in the management UI, but it's not exposed in the CR status.

Describe the solution you'd like

Expose in the CR status if a deprecated feature is used, or if not all stable feature flags are enabled.

Describe alternatives you've considered

Automatically enable all feature flags after a rolling update, or as post-deploy steps.