fix grafana prometheus docker-compose settings

Author: tzolov

src/grafana/prometheus/docker/docker-compose.yml

@@ -30,6 +30,7 @@ services:
     ports:
       - '8181:8181'
     environment:
+      - metrics.prometheus.target.filePath=/tmp/scdf-targets/targets.json
       - metrics.prometheus.target.discoveryUrl=http://${SCDF_HOST_IP}:9393/runtime/apps
       - metrics.prometheus.target.overrideIp=${SCDF_HOST_IP}