Adding API URL envvar for ECS config
# /var/run/docker.sock.
signalFxAccessToken: {"#from": "env:ACCESS_TOKEN"}
ingestUrl: {"#from": "env:INGEST_URL", optional: true}
+apiUrl: {"#from": "env:API_URL", optional: true}
intervalSeconds: {"#from": "env:INTERVAL_SECONDS", default: 10}
