[Autofill Assistant] Updated owners file to include new chromium committers on the team.

Bug: 806868
Change-Id: I8dabef308839aca8957226db91f7b98bae31c01e
Reviewed-on: https://chromium-review.googlesource.com/c/1489206
Commit-Queue: Clemens Arbesser <arbesser@google.com>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635932}

components/autofill_assistant/OWNERS

+# Please keep these in alphabetical order
+arbesser@google.com
 gogerald@chromium.org
+jdemeulenaere@chromium.org
 mcarlen@chromium.org
 rouslan@chromium.org
 szermatt@chromium.org