Improve get.sh script with similar features like istio quickstart has

[christian-kreuzberger-dtx]

Source: https://raw.githubusercontent.com/istio/istio/master/release/downloadIstioCandidate.sh

Examples:

Automatically determine version based on latest gh release

# Determine the latest Istio version by version number ignoring alpha, beta, and rc versions.
if [ "x${ISTIO_VERSION}" = "x" ] ; then
  ISTIO_VERSION="$(curl -sL https://github.com/istio/istio/releases | \
                  grep -o 'releases/[0-9]*.[0-9]*.[0-9]*/' | sort --version-sort | \
                  tail -1 | awk -F'/' '{ print $2}')"
  ISTIO_VERSION="${ISTIO_VERSION##*/}"
fi

if [ "x${ISTIO_VERSION}" = "x" ] ; then
  printf "Unable to get latest Istio version. Set ISTIO_VERSION env var and re-run. For example: export ISTIO_VERSION=1.0.4"
  exit;
fi

Print some helpful information on how to continue

printf ""
printf "\nIstio %s Download Complete!\n" "$ISTIO_VERSION"
printf "\n"
printf "Istio has been successfully downloaded into the %s folder on your system.\n" "$NAME"
printf "\n"
BINDIR="$(cd "$NAME/bin" && pwd)"
printf "Next Steps:\n"
printf "See https://istio.io/latest/docs/setup/install/ to add Istio to your Kubernetes cluster.\n"
printf "\n"
printf "To configure the istioctl client tool for your workstation,\n"
printf "add the %s directory to your environment path variable with:\n" "$BINDIR"
printf "\t export PATH=\"\$PATH:%s\"\n" "$BINDIR"
printf "\n"
printf "Begin the Istio pre-installation check by running:\n"
printf "\t istioctl x precheck \n"
printf "\n"
printf "Need more information? Visit https://istio.io/latest/docs/setup/install/ \n"