style(telemetry): keep the JMeter annotation colour as it was

Match the other dashboards: restore `rgb(70, 70, 70)` on `Perf Runs (JMeter)`
so regions that rendered before keep their colour. `Perf Runs (Locust)` stays
aqua.

docker/telemetry/grafana/dashboards/ledger-sync-health.json

@@ -20,7 +20,7 @@
         },
         "enable": true,
         "hide": false,
-        "iconColor": "rgb(144, 133, 233)",
+        "iconColor": "rgb(70, 70, 70)",
         "name": "Perf Runs (JMeter)",
         "target": {
           "limit": 100,