[shared storage] Implement interestGroup()

Add interestGroups() to the shared storage worklet, to return the
Protected Audience interest groups associated with the
shared storage origin's owner, with some additional metadata.

Implement this behind a runtime feature, which is implicitly
controlled by a Finch flag.

Explainer PR: https://github.com/WICG/shared-storage/pull/180

Spec PR(s):
1) https://github.com/WICG/turtledove/pull/1299
2) https://github.com/WICG/shared-storage/pull/203

Bug: 367992703
Binary-Size: Size increase is unavoidable.
Fuchsia-Binary-Size: Size increase is unavoidable.
Change-Id: I5fc5767fa53a91f021d64a871a6dd9cb88f4431c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5696046
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Yao Xiao <yaoxia@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1369483}