This results in a simpler service unit which doesn't first have to
start a shell:
> cat /nix/store/s95nsr8zbkblklanqpkiap49mkwbaq45-unit-alertmanager.service/alertmanager.service
...
ExecStart=/nix/store/4g784lwcy7kp69hg0z2hfwkhjp2914lr-alertmanager-0.16.2-bin/bin/alertmanager \
--config.file /nix/store/p2c7fyi2jkkwq04z2flk84q4wyj2ggry-checked-config \
--web.listen-address [::1]:9093 \
--log.level warn
...
739bdff4a4