[FLEDGE] Move a little more logic from AuctionRunner to Auction.

In particular, move ClosePipes() logic, logic to get IGs that made bids,
and debug report URLs.

Bug: 1288865
Change-Id: Ica15c2662ee4cc8a8347de498770d76b982fe11c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3446240


Reviewed-by: Maks Orlovich <morlovich@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968345}