Changes to Download multiple translated files

added the pattern ^[a-z0-9]{9}$ to the path request parameter projectId

added the pattern ^[a-z]{2}(-[A-Z]{2})?$ to the request property files/items/localeIds/items

the response property response/errors/items/details became nullable for the status 400

the response property response/errors/items/details became nullable for the status 401

the response property response/errors/items/details became nullable for the status 429

the response property response/errors/items/details became nullable for the status 500

the response property response/errors/items/key became nullable for the status 400

the response property response/errors/items/key became nullable for the status 401

the response property response/errors/items/key became nullable for the status 429

the response property response/errors/items/key became nullable for the status 500

endpoint added