Update chromeos/app_mode owners

Since customer kiosks are being deprecated, the only use of kiosks is
enterprise, who owns all the bugs related to them. Adding ChromeOS
Enterprise TL as an owner.

Change-Id: I24ce28317798bd2525438d25d6a90a510598f0e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1855743
Commit-Queue: Anatoliy Potapchuk <apotapchuk@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705482}

chrome/browser/chromeos/app_mode/OWNERS

+apotapchuk@chromium.org
+poromov@chromium.org
+
+# COMPONENT: UI>Shell>Kiosk