feat: add the ability to specify a custom mailto for all cron output

plugins/cron/set.go

@@ -0,0 +1,11 @@
+package cron
+
+import "errors"
+
+func validateSetValue(appName string, key string, value string) error {
+	if key == "mailto" && appName != "--global" {
+		return errors.New("Property cannot be specified on a per-app basis")
+	}
+
+	return nil
+}