crostestutils: add performance directory

Performance related test utilities are going through some deshelling
(huzzah).  This change provides a home for such utilities, such that
the maintainers (who know the performance tooling landscape) can own
their own destinies on maintenance costs.

I did not include chromeos-performance-eng@google.com in the OWNERS
list, as it is not associated with a gerrit user (a pre-requ per:
https://gerrit.googlesource.com/plugins/find-owners/+/main/src/main/resources/Documentation/syntax.md)

BUG=b:166744231
TEST=None

Change-Id: I6d42e23974529b5911b9439cfad9ebf03b4e8c87
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/2643240
Reviewed-by: Chinglin Yu <chinglinyu@chromium.org>
Reviewed-by: Kevin Shelton <kmshelton@chromium.org>
Commit-Queue: Kevin Shelton <kmshelton@chromium.org>
Tested-by: Kevin Shelton <kmshelton@chromium.org>
Auto-Submit: Kevin Shelton <kmshelton@chromium.org>