Add fetch configlet script (exercism#368)

* Add fetch configlet script

* Add CODEOWNER for fetch configlet script

.github/CODEOWNERS

@@ -3,3 +3,6 @@ config/maintainers.json @exercism/maintainers-admin
 
 # Code owners
 .github/CODEOWNERS      @exercism/maintainers-admin
+
+# Changes to `fetch-configlet` should be made in the `exercism/configlet` repo
+bin/fetch-configlet     @exercism/maintainers-admin

bin/fetch-configlet

@@ -0,0 +1,74 @@
+#!/usr/bin/env bash
+
+# This file is a copy of the
+# https://github.com/exercism/configlet/blob/main/scripts/fetch-configlet file.
+# Please submit bugfixes/improvements to the above file to ensure that all tracks benefit from the changes.
+
+set -eo pipefail
+
+readonly LATEST='https://api.github.com/repos/exercism/configlet/releases/latest'
+
+case "$(uname)" in
+  Darwin*)   os='mac'     ;;
+  Linux*)    os='linux'   ;;
+  Windows*)  os='windows' ;;
+  MINGW*)    os='windows' ;;
+  MSYS_NT-*) os='windows' ;;
+  *)         os='linux'   ;;
+esac
+
+case "${os}" in
+  windows*) ext='zip' ;;
+  *)        ext='tgz' ;;
+esac
+
+case "$(uname -m)" in
+  *64*)  arch='64bit' ;;
+  *686*) arch='32bit' ;;
+  *386*) arch='32bit' ;;
+  *)     arch='64bit' ;;
+esac
+
+curlopts=(
+  --silent
+  --show-error
+  --fail
+  --location
+  --retry 3
+)
+
+if [[ -n "${GITHUB_TOKEN}" ]]; then
+  curlopts+=(--header "authorization: Bearer ${GITHUB_TOKEN}")
+fi
+
+suffix="${os}-${arch}.${ext}"
+
+get_download_url() {
+  curl "${curlopts[@]}" --header 'Accept: application/vnd.github.v3+json' "${LATEST}" |
+    grep "\"browser_download_url\": \".*/download/.*/configlet.*${suffix}\"$" |
+    cut -d'"' -f4
+}
+
+main() {
+  if [[ -d ./bin ]]; then
+    output_dir="./bin"
+  elif [[ $PWD == */bin ]]; then
+    output_dir="$PWD"
+  else
+    echo "Error: no ./bin directory found. This script should be ran from a repo root." >&2
+    return 1
+  fi
+
+  download_url="$(get_download_url)"
+  output_path="${output_dir}/latest-configlet.${ext}"
+  curl "${curlopts[@]}" --output "${output_path}" "${download_url}"
+
+  case "${ext}" in
+    *zip) unzip "${output_path}" -d "${output_dir}"   ;;
+    *)    tar xzf "${output_path}" -C "${output_dir}" ;;
+  esac
+
+  rm -f "${output_path}"
+}
+
+main