Programmatic server restart

[mzy2240]

As discussed in #122 (comment), I think from a reliability perspective it makes sense to provide the capability to restart the server, either in a scheduled (cron) fashion or triggered by an external script. If it is doable, it might worth to consider persistent state as the second step. But for now, according to the discussion, it feels Oxygen.jl still lack the capability for programmatic restart, even at the risk of losing state.