Add hack/update-ubuntu-image.sh

```console
$ hack/update-ubuntu-image.sh --help
update-ubuntu-image.sh: Update the Ubuntu image location in the specified templates

Usage:
  update-ubuntu-image.sh [--minimal|--server] [--version <version>] <template.yaml>...

Description:
  This script updates the Ubuntu image location in the specified templates.
  If the image location in the template contains a release date in the URL, the script replaces it with the latest available date.
  If no flags are specified, the script uses the flavor and version from the image location basename in the template.

  Image location basename format: ubuntu-<version>-<flavor>-cloudimg-<arch>.img

  Released Ubuntu image information is fetched from the following URLs:

    Server: https://cloud-images.ubuntu.com/releases/stream/v1/com.ubuntu.cloud:released:download.json
    Minimal: https://cloud-images.ubuntu.com/minimal/releases/stream/v1/com.ubuntu.cloud:released:download.json

  The downloaded JSON file will be cached in the Lima cache directory.

Examples:
  Update the Ubuntu image location in templates/**.yaml:
  $ update-ubuntu-image.sh templates/**.yaml

  Update the Ubuntu image location in ~/.lima/ubuntu/lima.yaml:
  $ update-ubuntu-image.sh ~/.lima/ubuntu/lima.yaml

  Update the Ubuntu image location to ubuntu-24.04-minimal-cloudimg-<arch>.img in ~/.lima/docker/lima.yaml:
  $ update-ubuntu-image.sh --minimal --version 24.04 ~/.lima/docker/lima.yaml

Flags:
  --server             Use the server flavor image
  --minimal            Use the minimal flavor image
  --version <version>  Use the specified version
  -h, --help           Print this help message
```

Signed-off-by: Norio Nomura <[email protected]>

Author: norio-nomura

hack/cache-common-inc.sh

@@ -216,6 +216,26 @@ function location_to_sha256() {
 	)
 }
 
+# e.g.
+# ```console
+# $ cache_download_dir
+# .download # on GitHub Actions
+# /home/user/.cache/lima/download # on Linux
+# /Users/user/Library/Caches/lima/download # on macOS
+# /home/user/.cache/lima/download # on others
+# ```
+function cache_download_dir() {
+	if [[ ${GITHUB_ACTIONS:-false} == true ]]; then
+		echo ".download"
+	else
+		case "$(uname -s)" in
+		Linux) echo "${XDG_CACHE_HOME:-${HOME}/.cache}/lima/download" ;;
+		Darwin) echo "${HOME}/Library/Caches/lima/download" ;;
+		*) echo "${HOME}/.cache/lima/download" ;;
+		esac
+	fi
+}
+
 # e.g.
 # ```console
 # $ location_to_cache_path "https://cloud-images.ubuntu.com/releases/24.04/release-20240809/ubuntu-24.04-server-cloudimg-arm64.img"
@@ -224,7 +244,7 @@ function location_to_sha256() {
 function location_to_cache_path() {
 	local location=$1
 	[[ ${location} != "null" ]] || return
-	sha256=$(location_to_sha256 "${location}") && echo ".download/by-url-sha256/${sha256}"
+	sha256=$(location_to_sha256 "${location}") && download_dir=$(cache_download_dir) && echo "${download_dir}/by-url-sha256/${sha256}"
 }
 
 # e.g.
@@ -321,3 +341,48 @@ function hash_file() {
 		echo "${hash}" | xxd -r -p | sha256sum | cut -d' ' -f1
 	)
 }
+
+# Download the file to the cache directory and print the path.
+# e.g.
+# ```console
+# $ download_to_cache "https://cloud-images.ubuntu.com/releases/24.04/release-20240821/ubuntu-24.04-server-cloudimg-arm64.img"
+# .download/by-url-sha256/346ee1ff9e381b78ba08e2a29445960b5cd31c51f896fc346b82e26e345a5b9a/data # on GitHub Actions
+# /home/user/.cache/lima/download/by-url-sha256/346ee1ff9e381b78ba08e2a29445960b5cd31c51f896fc346b82e26e345a5b9a/data # on Linux
+# /Users/user/Library/Caches/lima/download/by-url-sha256/346ee1ff9e381b78ba08e2a29445960b5cd31c51f896fc346b82e26e345a5b9a/data # on macOS
+# /home/user/.cache/lima/download/by-url-sha256/346ee1ff9e381b78ba08e2a29445960b5cd31c51f896fc346b82e26e345a5b9a/data # on others
+function download_to_cache() {
+	local code_time_type_url
+	code_time_type_url=$(
+		curl -sSLI -w "%{http_code}\t%header{Last-Modified}\t%header{Content-Type}\t%{url_effective}" "$1" -o /dev/null
+	)
+
+	local code time type url
+	IFS=$'\t' read -r code time type url filename <<<"${code_time_type_url}"
+	[[ ${code} == 200 ]] || exit 1
+
+	local cache_path
+	cache_path=$(location_to_cache_path "${url}")
+	[[ -d ${cache_path} ]] || mkdir -p "${cache_path}"
+
+	local needs_download=0
+	[[ -f ${cache_path}/data ]] || needs_download=1
+	[[ -f ${cache_path}/time && "$(<"${cache_path}/time")" == "${time}" ]] || needs_download=1
+	[[ -f ${cache_path}/type && "$(<"${cache_path}/type")" == "${type}" ]] || needs_download=1
+	if [[ ${needs_download} -eq 1 ]]; then
+		local code_time_type_url_filename
+		code_time_type_url_filename=$(
+			echo "downloading ${url}" >&2
+			curl -SL -w "%{http_code}\t%header{Last-Modified}\t%header{Content-Type}\t%{url_effective}\t%{filename_effective}" --no-clobber -o "${cache_path}/data" "${url}"
+		)
+		local filename
+		IFS=$'\t' read -r code time type url filename <<<"${code_time_type_url_filename}"
+		[[ ${code} == 200 ]] || exit 1
+		[[ "${cache_path}/data" == "${filename}" ]] || mv "${filename}" "${cache_path}/data"
+		# sha256.digest seems existing if expected digest is available. so, not creating it here.
+		# sha256sum "${cache_path}/data" | awk '{print "sha256:"$1}' >"${cache_path}/sha256.digest"
+		echo -n "${time}" >"${cache_path}/time"
+	fi
+	[[ -f ${cache_path}/type ]] || echo -n "${type}" >"${cache_path}/type"
+	[[ -f ${cache_path}/url ]] || echo -n "${url}" >"${cache_path}/url"
+	echo "${cache_path}/data"
+}