Changes to Find custom fields for specified project

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

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 404

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 404

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