Interface to retrieve applied k-anon parameters

[JacobGo]

As Chrome incrementally rolls out k-anonymity enforcement and parameter tuning per the documented timeline, we request an interface to retrieve the currently applied k-anonymity parameters. This will be used by adtechs to evaluate the precise impact of each k-anon step on their Protected Audience API integrations. An explicit browser-level interface is required because Chrome's rollout only impacts a gradually increasing fraction of all traffic.

The desired interface would be similar to cookie deprecation labels. The browser could provide a label string corresponding to the current step in the k-anon rollout (k_anon_1), or preferably an object containing the exact parameters (query update period p, counting window length w, and k-anon threshold k). Absence of the API may be interpreted as missing k-anon enforcement or waiting for a pending k-anon query.

[JacobGo]

For the initial k-anon rollout and while this feature request is under consideration, we intend to interpret navigator.deprecatedRunAdAuctionEnforcesKAnonymity as applying the documented parameters of k=10, p=12h, and w=30d. However, after 3PCD begins, we anticipate a need for the more granular proposed API.