Add correct After targets for prometheus_exporters

arch-audit hung as it was started before there was a working internet
connection. To work around this issue, add proper Wants/After targets
for network-online.target and for the rebuilderd textcollector let it
start after rebuilderd.service is "online".
2 jobs for add_target_prometheus_exporters in 39 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Test
passed ansible-lint #15396

00:00:39

passed terraform-validate #15397

00:00:25