Add optional attribute to specification fields

- `auxiliary-info` is specified as an optional field.

- `lvcnrcheck` gives a return code of `0` if the only failing fields are
  option and missing.

  However if fields are present and fail for other reasons (for example
  wrong type such as `str` when it should be `int`) then the return code
  will be `1`.
1 job for allow-optional-fields in 1 minute and 55 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #917
test

00:01:55