List rejection reasons

Rejection reasons are the organization-defined dictionary of outcomes recorded when an application is rejected (e.g. Not a cultural fit, Lacking skill(s)/qualification(s), Wasn't interested, Didn't like offer, Spam). Each rejected application references one of these through its rejection_details.rejection_reason; this endpoint is the source of truth for the picklist itself. Reasons are grouped under a type of We rejected them, They rejected us, None specified, or Security concern — use the type to distinguish the organization declining the candidate from the candidate withdrawing, and to identify trust/fraud outcomes in reporting. Customized per organization under Configure > Custom Options > Rejection Reasons, so the available set varies between Greenhouse accounts; pass include_defaults=true to also return the standard reasons that ship with every account. Reasons of type Security concern are only returned when the enable_reject_as_security_concern product flag is on. Distinct from rejection_details, which carries the per-application rejection instance attached to a rejected application, and from close_reasons, which apply to openings rather than applications.