Replaces the vendored Go exporter with two pre-built upstream images:
- quay.io/prometheuscommunity/json-exporter:v0.7.0 maps the gateway JSON
into prometheus metrics via JSONPath. The G4AR keys signal blocks as
"5g" / "4g" (digit-prefixed), which the k8s client-go JSONPath dialect
only reaches via bracket-with-single-quote notation.
- nginxinc/nginx-unprivileged:1.27-alpine-slim sidecar rewrites
GET /metrics → GET /probe?module=tmhi&target=http://192.168.12.1/...
so the existing kubernetes-services scrape job picks it up over the
apiserver proxy with no Prometheus-side config changes.
Avoiding caddy here: its binary carries cap_net_bind_service file caps,
which the kernel refuses to exec under no_new_privs as a non-root user.
Dashboard "Gateway up" panel now reads up{service="tmobile-exporter"}
(Prometheus's built-in scrape-success gauge) since json_exporter's
/probe endpoint does not emit probe_success.
15 panels covering gateway up/uptime, 4G/5G bars, and per-band
RSRP/RSRQ/SNR/RSSI time series. Sources metrics from the new
tmobile-exporter (job=tmobile_gateway).
