[Feature request] Add a CLI option to successfully exit on any non-5xx response

Hi,

I would like to use `wait-on` to check that a REST API (that I did not write) is online, but without triggering an API endpoint that runs actions. It doesn't have a `/ping` endpoint or anything, so just calling `/` which will return 404 should do it.

But, there's currently no CLI option to consider a non-2xx response valid.

Thanks

No files or tests are identified in the issue. Start by locating the CLI option parsing and the HTTP response validation used by wait-on; the change is complete when a CLI option makes any non-5xx response, including 404, exit successfully while 5xx responses remain unsuccessful.

Written by the indexing model from the issue text.