Add myself ot OTS OWNERS

My intention was to do that already in [1] but I somehow missed adding
my own email address.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2590037

Bug: 1158389
Change-Id: I6c2ddb4a9e8e62ae3a83487d27a19c1ab8c2f439
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2636353Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844628}

third_party/ots/OWNERS

 bashi@chromium.org
 bungeman@chromium.org
+drott@chromium.rg
 jshin@chromium.org
 kojii@chromium.org