fix shebang in generated script

Index: plugins/opensearch-security/tools/install_demo_configuration.sh
--- plugins/opensearch-security/tools/install_demo_configuration.sh.orig
+++ plugins/opensearch-security/tools/install_demo_configuration.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 #install_demo_configuration.sh [-y]
 
 UNAME=$(uname -s)
@@ -9,6 +9,8 @@ elif [ "$UNAME" = "Darwin" ]; then
 else
   OS="other"
 fi
+
+JAVA_HOME="$(${TRUEPREFIX}/bin/javaPathHelper -h opensearch)"
 
 SCRIPT_PATH="${BASH_SOURCE[0]}"
 if ! [ -x "$(command -v realpath)" ]; then
