add packaging script

Author: facchinm

extra/package.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+if [ ! -f platform.txt ]; then
+  echo Launch this script from the root core folder as ./extras/package.sh VERSION
+  exit 2
+fi
+
+VERSION=$1
+
+tar  --exclude=extras/** --exclude=.git* --exclude=build --exclude=venv --exclude=samples -cjhf ../arduino-core-zephyr-llext-${VERSION}.tar.bz2 .