chore(policy): add set_version.sh script

#!/usr/bin/env bash

set -eu

if (( $# != 1 )); then

  echo "Usage: set_version.sh <version>" >&2

  exit 1

fi

version="$1"

if [ "$(git status --untracked-files=no --porcelain)" ]; then

    printf "Uncommitted changes in tracked files.\nPlease commit first and then run the script!\n"

    exit 0;

fi

./mvnw versions:set versions:commit -DnewVersion="${version}"

git commit -am "release(policy): ${version}"