pkg: add example script to create tarball with submodules instantiated

In preparation for packaging of tls_wolfssl, add an example script to
create source tarball with submodule code.

pkg/scripts/git-archive-all.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# packaging script to include submodules
+# modified from: https://gist.github.com/arteymix/03702e3eb05c2c161a86b49d4626d21f
+# Usage: pkg/scripts/git-archive-all.sh kamailio-5.8.0 ../output/kamailio-5.8.0_src
+
+usage() {
+    echo Usage:  pkg/scripts/git-archive-all.sh kamailio-5.8.0 ../output/kamailio-5.8.0_src
+}
+
+if [ -z $1 ]; then
+    echo "You must specify a prefix name."
+    usage
+    exit 1
+fi
+
+if [ -z $2 ]; then
+    echo "You must specify a super-archive name."
+    usage
+    exit 1
+fi
+
+git archive --prefix "$1/" -o "$2.tar" HEAD
+git submodule foreach --recursive "git archive --prefix=$1/\$sm_path/ --output=\$sha1.tar HEAD && tar --concatenate --file=$(pwd)/$2.tar \$sha1.tar && rm \$sha1.tar"
+
+gzip "$2.tar"