Secure actuator endpoints

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

At the moment the actuator and metrics endpoints are reachable via the default application port.
This means everyone can access all these endpoints.

**Describe the solution you'd like**

Use a custom management port which is only used internally and can't be accessed externally.
Since the `/actuator/info` endpoint is also affected by this, it must be considered how to deal with this in the future, e.g. for the appswitcher.