Move aggregator into its own repo and add it to the image

conf/init/service/prometheus-aggregator/log/run

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+# Ensure dependencies start before the logger
+sv check syslog-ng > /dev/null || exit 1
+
+# Start the logger
+exec logger -i -t prometheus-aggregator

conf/init/service/prometheus-aggregator/run

@@ -0,0 +1,7 @@
+#! /bin/bash
+
+echo 'Starting prometheus aggregator'
+
+/usr/local/bin/prometheus-aggregator
+
+echo 'Prometheus aggregator exited'