Add CPU unit to resource specification

Introduce an explicit CPU unit concept in the resource specification (e.g. finer-grained CPU quantity/unit handling in resource slots and policies). Exact semantics and migration defined by the BEP.

JIRA Issue: BA-7027

Start by locating the resource specification, resource slots, and policies, then read the BEP referenced in the issue for the CPU unit semantics and migration requirements. Done means the explicit CPU unit concept is implemented consistently across those areas according to the BEP, with the required migration behavior verified.

Written by the indexing model from the issue text.