Wire up prom_ex with built-in Application, Beam, Phoenix, PhoenixLiveView,
and Ecto plugins, plus a custom plugin that exposes the existing
app-specific telemetry (packet pipeline, spatial PubSub, repo pool,
postgres stats, insert optimizer) as Prometheus metrics.
Mount PromEx.Plug at /metrics — internal-only, intended to be scraped
by the cluster's external Prometheus through the kube-apiserver pod
proxy. K8s pod template now carries prometheus.io/{scrape,port,path}
annotations so the existing kubernetes-pods scrape job picks it up
automatically.
PromEx is disabled in the test environment.
Also harden the packet cleanup and partition manager tests with
Repo.delete_all setup hooks so they aren't poisoned by residual rows
committed outside a sandbox transaction in earlier runs (which were
inflating delete counts and triggering ATTACH PARTITION check_violation
errors against packets_default).