chore: add hack/latest_version.sh

Add script to lookup component version from github releases.

To sort, we're using sort -V or --version-sort, depending which
option is available. This which has some limitations:
- pre-releases (-) are sorted as post-releases
- post-releases and build metadata (+) are ignored

This is the best option available for SemVer sorting without
requiring the user to install additional depedencies, like nodejs.

hack/latest_version.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+# Copyright 2024 The Kubernetes Authors.
+# SPDX-License-Identifier: Apache-2.0
+
+# Looks up and prints the latest release version of the specified component.
+# The first arg should be the component name (tag prefix).
+#
+# Requires GNU sort (or gsort) for version sorting.
+
+set -euo pipefail
+
+component="${1:-}"
+if [ -z "${component}" ]; then
+    echo >&2 "The first argument should be the requested component name."
+    exit 2
+fi
+
+# Prefer gsort, if installed, to support coreutils install on mac with homebrew.
+if command -v gsort >/dev/null 2>&1; then
+    SORT="gsort"
+elif command -v sort >/dev/null 2>&1; then
+    SORT="sort"
+else
+    echo >&2 "sort (or gsort) required on the PATH for version sorting."
+    exit 1
+fi
+# Validate sort has the -V or --version-sort option
+if ${SORT} --help 2>&1 | grep -qe '\-\-version-sort'; then
+    # GNU sort & BSD sort have both -V and --version-sort
+    # Recent Mac sort has --version-sort, but not -V
+    VERSION_FLAG="--version-sort"
+elif ${SORT} --help 2>&1 | grep -qe '^[[:space:]]*\-V[[:space:]]*'; then
+    # BusyBox sort has -V but not --version-sort
+    VERSION_FLAG="-V"
+else
+    # Older Mac sort has neither -V nor --version-sort
+    echo >&2 "sort (or gsort) on the PATH must support version sort (-V or --version-sort)."
+    if "$(uname)" == "Darwin"; then
+        echo >&2 "On Mac, either update the OS or use Homebrew to install the coreutils package, which includes GNU sort as gsort."
+    elif "$(uname)" == "Linux"; then
+        echo >&2 "On Linux, install the latest version of GNU or BSD sort."
+    fi
+    exit 1
+fi
+
+# We can't use /releases/latest because the desired component may not be the
+# last component released.
+RELEASES_URL="https://api.github.com/repos/kubernetes-sigs/kustomize/releases"
+
+# You can authenticate by exporting the GITHUB_TOKEN in the environment
+if [[ -z "${GITHUB_TOKEN:-}" ]]; then
+    RELEASES_JSON=$(curl -s "$RELEASES_URL")
+else
+    RELEASES_JSON=$(curl -s "$RELEASES_URL" --header "Authorization: Bearer ${GITHUB_TOKEN}")
+fi
+
+if [[ "${RELEASES_JSON}" == *"API rate limit exceeded"* ]]; then
+  echo "Github rate-limiter failed the request. Either authenticate or wait a couple of minutes."
+  exit 1
+fi
+
+# This would be better with jq, but we're using grep and cut to avoid the
+# dependency, even though it might be more fragile.
+echo "${RELEASES_JSON}" \
+    | grep -o "\"tag_name\": \"${component}/.*\"" \
+    | cut -d\" -f4 | cut -d/ -f2 \
+    | ${SORT} ${VERSION_FLAG} | tail -1