Populate additional OWNERS files.

This incorporates owner assignments from go/secportageowners into the
tree.

BUG=None
TEST=None

Change-Id: I54a23c67d8dd5927767cf9b5f171e24cf1157d15
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2414048
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mattias Nissler <mnissler@chromium.org>