Add an exec daemon plugin (#4424)

plugins/inputs/execd/examples/count.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+## Example in bash using STDIN signaling
+
+counter=0
+
+while read; do
+    echo "counter_bash count=${counter}"
+    let counter=counter+1
+done
+
+(>&2 echo "terminate")