cros-test: also copy cipd uv binary to /opt/browser-tools

Chromium is migrating the root vpython config to vpython.toml (uv backend).
When running under FlowUV, vpython3 requires the uv binary in the sibling
directory uv/.

The CIPD package infra/tools/luci/vpython3/${platform} bundles uv/ alongside
vpython3, 3.8/, and 3.11/. Currently, cros-test Dockerfile only moves
vpython3, 3.8/, and 3.11/ to /opt/browser-tools/, leaving uv/ behind
in /usr/bin/.

Move /usr/bin/uv/ to /opt/browser-tools/uv/ so vpython3 can resolve
the uv binary when running FlowUV inside cros-test containers.

BUG=40942322
TEST=None
TAG=agy
CONV=b53bdf70-37e7-4696-be50-8ee6fc19b1f8

Change-Id: Icd2cfb4f86149164fcc7f3e43ed79f7ad756b076
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/8404605
Tested-by: Alex Ovsienko <ovsienko@google.com>
Commit-Queue: Alex Ovsienko <ovsienko@google.com>
Auto-Submit: Alex Ovsienko <ovsienko@google.com>
Reviewed-by: Terry Yan <yichiyan@google.com>