Add brunoad to kiosk_next OWNERS

Bruno is now a committer, so let's add him to OWNERS.

Bug: None
Change-Id: I2cabe8ed980396db6dda7b68e663f0ba6da93a61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1597019
Auto-Submit: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Lucas Tenório <ltenorio@chromium.org>
Commit-Queue: Bruno Santos <brunoad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656932}

ash/kiosk_next/OWNERS

 agawronska@chromium.org
+brunoad@chromium.org
 ltenorio@chromium.org
 michaelpg@chromium.org