Bidder worklet will not provide interestGroupName when k-anon enforced.

Changes bidder worklet to match spec by not providing the
interestGroupName field when k-anonymity enforcement would prevent the
field from being available. Also adds a metric to measure how often we
are not including the reporting ID due to k-anonymity enforcement.

Change-Id: I45c38f668477ea65e9ccff366b3b912e68e202bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402314


Commit-Queue: Russ Hamilton <behamilton@google.com>
Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Reviewed-by: Orr Bernstein <orrb@google.com>
Cr-Commit-Position: refs/heads/main@{#1280715}