chore: add clear.sh tool for clearing retained messages in MQTT broker

.gitignore

@@ -27,7 +27,6 @@ npm-debug.log
 NOTES
 coverage/
 dist/
-tools/
 
 # Apple
 .DS_Store

tools/clear.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+mosquitto_sub -h mosquitto.graystorm.com -v -t '#' --retained-only \
+  | grep 'amcrest2mqtt' \
+  | while read -r topic payload ; do
+      mosquitto_pub -h mosquitto.graystorm.com -t "$topic" -n -r
+      echo "Purged $topic"
+    done
+echo "done."