Revisit support of SKAdNetwork in Bidding Only integration

[YuriyVelichkoPI]

Motivation

Publishers who integrate the Bidding Only scenario (Original API) often ask for supporting SKAdNetwork.

Background

Some time ago, we tried to implement SKAdNetwork with Original API (#342).

That time, it was impossible since the SKAdNetwork depends on the click event. And in the scope of Bidding Only integration, the Prebid SDK doesn't manage clicks. We tried several workarounds but didn't find any reliable ones (details in the issue and related PRs above).

Objectives

Take a fresh look on SKAdNetwork and Bidding Only integration and try to find a way to support SKAdNetwork.