All four sibling swarm containers import swarm-container-resolver.nix;
this one did not. It matters more here than most: otel.endpoint is an
operator-configured external hostname, and reaching it is the entire
reason this container holds a credential.
Also aligns two details with those siblings - the enable default is
asserted from swarm-required-services.nix with the metrics pair it
feeds, so that file remains the one place a service host is declared,
and machine is readOnly since its description already calls it a fact
rather than a knob.
28623e5eff