bin(upload-legacy-assets): add script (#728)

Add a script for uploading assets that are required by old
`fetch-configlet` scripts. We can remove this script later.

See 57e6c5f (".github, fetch-configlet: rename release assets")
for context.

Track CI no longer requires the linux asset with the old name to
exist [1].

The assets in the latest release [2] at the time of writing:

    configlet-linux-64bit.tgz
    configlet-mac-64bit.tgz
    configlet-windows-64bit.zip
    configlet_4.0.0-beta.9_checksums_sha256.txt
    configlet_4.0.0-beta.9_linux_x86-64.tar.gz
    configlet_4.0.0-beta.9_macos_x86-64.tar.gz
    configlet_4.0.0-beta.9_windows_x86-64.zip

[1] exercism/github-actions@a63d5ca89437
[2] https://github.com/exercism/configlet/releases/tag/4.0.0-beta.9

bin/upload-legacy-assets

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+
+err() {
+  echo "$*" >&2
+}
+
+main() {
+  if [[ "$#" -eq 1 ]]; then
+    local tmp_dir='upload-assets-tmp'
+    local repo='github.com/exercism/configlet'
+    local tag="$1"
+    local arch='x86-64'
+    local pattern="*${arch}*"
+    mkdir -v -p "${tmp_dir}"
+    cd "${tmp_dir}"
+    gh -R "${repo}" release download "${tag}" -p "${pattern}"
+    declare -A assets=(
+      ["configlet_${tag}_linux_${arch}.tar.gz"]='configlet-linux-64bit.tgz'
+      ["configlet_${tag}_macos_${arch}.tar.gz"]='configlet-mac-64bit.tgz'
+      ["configlet_${tag}_windows_${arch}.zip"]='configlet-windows-64bit.zip'
+    )
+    for k in "${!assets[@]}"; do
+      mv -v "${k}" "${assets[${k}]}"
+    done
+    gh -R "${repo}" release upload "${tag}" "${assets[@]}"
+    echo "After undrafting the new release, you can delete the assets with the old names"
+    echo "from the previous release"
+  else
+    err "You must call this script with exactly one argument."
+    err "Usage:"
+    err "  upload-legacy-assets <tag>"
+    exit 1
+  fi
+}
+
+main "$@"