systemd: set NotifyAccess=all

Problem: processes other than the main one cannot send systemd
status updates, but flux-dump(1) would like to do so.

Set NotifyAccess=all instead of NotifyAccess=main to allow all
members of the service's control group to send updates.

Author: garlick

etc/flux.service.in

@@ -4,7 +4,7 @@ Wants=munge.service
 
 [Service]
 Type=notify
-NotifyAccess=main
+NotifyAccess=all
 TimeoutStopSec=90
 KillMode=mixed
 ExecStart=/bin/bash -c '\