adding node exporter, loki, and promtail

addon-prometheus/rootfs/etc/services.d/prometheus-configgen/run

@@ -0,0 +1,13 @@
+#!/command/with-contenv bashio
+bashio::log.info 'Starting prometheus config generator...'
+
+if ! bashio::fs.directory_exists /share/prometheus/targets; then
+  mkdir -p /share/prometheus/targets
+  chown -R prometheus:prometheus /share/prometheus/targets
+fi
+
+cd /opt/prometheus-configgen || bashio::exit.nok \
+  "Could not change working directory for prometheus-configgen."
+
+# Run Prometheus
+exec s6-setuidgid prometheus python3 combiner