Update radicale.service with upstream recommendations
    
    Follow most recommendations at https://radicale.org/3.0.html#tutorials/running-as-a-service/linux-with-systemd-system-wide:

    - Use more/stricter security settings

    - Use ReadWritePaths=/var/lib/radicale/ to support git hooks as reported in https://github.com/Kozea/Radicale/issues/1153

    - Adjust Restart policy