Update `generate-stackbrew-library.sh` to support `BASHBREW_LIBRARY` for easier cascading updates

See https://github.com/docker-library/official-images/pull/17640#issuecomment-2380308790

generate-stackbrew-library.sh

@@ -44,17 +44,19 @@ dirCommit() {
 
 getArches() {
 	local repo="$1"; shift
-	local officialImagesUrl='https://github.com/docker-library/official-images/raw/master/library/'
+	local officialImagesBase="${BASHBREW_LIBRARY:-https://github.com/docker-library/official-images/raw/HEAD/library}/"
 
-	eval "declare -g -A parentRepoToArches=( $(
-		find -name 'Dockerfile' -exec awk '
+	local parentRepoToArchesStr
+	parentRepoToArchesStr="$(
+		find -name 'Dockerfile' -exec awk -v officialImagesBase="$officialImagesBase" '
 				toupper($1) == "FROM" && $2 !~ /^('"$repo"'|scratch|.*\/.*)(:|$)/ {
-					print "'"$officialImagesUrl"'" $2
+					printf "%s%s\n", officialImagesBase, $2
 				}
 			' '{}' + \
 			| sort -u \
-			| xargs bashbrew cat --format '[{{ .RepoName }}:{{ .TagName }}]="{{ join " " .TagEntry.Architectures }}"'
-	) )"
+			| xargs -r bashbrew cat --format '["{{ .RepoName }}:{{ .TagName }}"]="{{ join " " .TagEntry.Architectures }}"'
+	)"
+	eval "declare -g -A parentRepoToArches=( $parentRepoToArchesStr )"
 }
 getArches 'postgres'