Returns all benefit deduction types available in the system. Each deduction type describes a category of payroll deduction (e.g. 401(k), HSA, Section 125) along with its allowable benefit plan types, default deduction code, and optional sub-types. Some deduction types are grouped under a parent with sub-types (e.g. Pre-Tax groups Health, Dental, etc.); in that case the parent entry has a non-empty subTypes array. Requires Benefits Administration permissions.