Add CPU and RAM usage to Metrics (#6968)

* Add CPU usage to Metrics

* Add RAM usage and rename to system-stats

* Shellcheck

* Remove SC exception

* Address review comments

scripts/system-stats.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+#
+# Reports cpu and ram usage statistics
+#
+set -e
+
+[[ $(uname) == Linux ]] || exit 0
+
+# need to cd like this to avoid #SC1091
+cd "$(dirname "$0")/.."
+source scripts/configure-metrics.sh
+
+while true; do
+  # collect the total cpu usage by subtracting idle usage from 100%
+  cpu_usage=$(top -bn1 | grep '%Cpu(s):' | sed "s/.*, *\([0-9.]*\)%* id.*/\1/" | awk '{print 100 - $1}')
+  # collect the total ram usage by dividing used memory / total memory
+  ram_total_and_usage=$(top -bn1 | grep 'MiB Mem'| sed "s/.*: *\([0-9.]*\)%* total.*, *\([0-9.]*\)%* used.*/\1 \2/")
+  read -r total used <<< "$ram_total_and_usage"
+  ram_usage=$(awk "BEGIN {print $used / $total * 100}")
+
+  report="cpu_usage=$cpu_usage,ram_usage=$ram_usage"
+  ./scripts/metrics-write-datapoint.sh "system-stats,hostname=$HOSTNAME $report"
+  sleep 1
+done