Allow separate privacy budgets for embedded domains

[linnan-github]

Currently many of ARA’s privacy budgets are partitioned via top-level sites. For most use-cases, it’s intended that embedded third-parties share a privacy budget. However, there are some use cases where this may lead to unintended sharing of those budgets (for example, AMP pages rendered by an AMP cache/viewer provider).

To mitigate this issue, in the short term we can allow separate privacy budgets for the embedded domain for specific use-cases.

We’re also exploring additional long-term solutions.

[Asask-sized]

#1457
#485
#1448
#1492
#git_commit