Move startup scripts to /etc/s6-overlay/startup.d
oneshot service named "startup" from underlying image executes
all files in /etc/s6-overlay/startup.d in alphabetical order
Remove various oneshot scripts from longrun service dependencies
Add "startup" oneshot service to longrun service dependencies
03-remove-mlathub-up deletes /run/mlathub_up when the container stops
As this file is created by the mlat-client service, remove it instead in
a finish script for mlat-client which is run when the mlat-client
service is stopped
02-remove-prometheus-data deletes /run/readsb-prometheus.prom when
the container stops
As this file is created by readsb, remove it instead in a finish script
for readsb which is run when the readsb service is stopped
