Add builder for Win11 bots in UAC pool.

1) Modify `waterfalls.pyl`.
2) Run `vpython3 .\testing\buildbot\generate_buildbot_json.py` to
re-generate `chromium.updater.json`.
3) Modify `chromium.updater.star` to add the builder. Run
`lucicfg fmt .\infra\config\subprojects\chromium\ci\chromium.updater.star` if
necessary.
4) Run `lucicfg infra\config\main.star`.

Bug: 1225352
Change-Id: I2eddb6831ef3e5fb7a682e7142ed6cdcea94a61d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3864352


Reviewed-by: Hans Wennborg <hans@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Xiaoling Bao <xiaolingbao@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1042260}