Is your feature related to a problem?

A proper system service app should not be running with full privileges and should fork as soon as soon as the initial startup sequence is completed and drop all privileges.

A "daemonized" service can be also more easily managed via systemd.

Describe the feature you'd like

As a follow up to #6204

Add the -d, --daemonize option to HOPRd that will allow the application to fork and run as a daemon with all privileges dropped, which is a standard practice.

This can be implemented via https://crates.io/crates/daemonize/

This obviously does not apply to Windows, which is not currently a supported platform anyways.