Adding in Logic to hold Split 1/3 - InitPhase

This sets up the underlying metric object to hold the required data
across the flow for the PreCandidate split - known as the InitialPhase. This will be a part of the
setup of the V3 metrics.

Bug: 270403549
Test: To be chained in, building for now
Change-Id: Idbc376cf79d0a7054192d66337ba1ff4cc82ca61