Adding isPrimary to Final Phase Metrics

This captures, for any API flows, if the chosen provider was the primary
provider. It's the first of a few changes that capture these additional
details and smaller API metrics.

Bug: 271135048
Test: Build and Won't Submit without E2E Test
Change-Id: Ib3870fb1f1f0ce870dd05bc1fc3901b5ef9e8200