Allow keepalived to be run as a non root user

[`keepalived-non-root.service`](https://github.com/acassen/keepalived/blob/master/keepalived/keepalived-non-root.service.in) allows keepalived to be run as a non root user, but with specific added capabilities to allow all the functionality that keepalived needs.

Created from https://gitlab.com/hifis/ansible/keepalived-role/-/issues/38