gcx is the Grafana Cloud CLI (dashboards, datasources, SLOs, synthetic
monitoring, alerts), used against the Citrix Grafana stack.
Pull it from nixpkgs-unstable via the existing overlay rather than the pinned
channel: 26.05 ships 0.2.14, which predates the stacks/contexts configuration
model and the agento11y commands, so the current tooling and docs do not apply
to it.