api: Add myself to OWNERS

As discussed offline, adding myself to OWNERS for the C++ GC, handles,
and Blink embedding issues in general.

Bug: chromium:1056170
Change-Id: Iff6a9f119000c04b40fb12b70f56d9bab7e32b43
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2116204Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66849}

include/OWNERS

 adamk@chromium.org
 danno@chromium.org
+mlippautz@chromium.org
 ulan@chromium.org
 verwaest@chromium.org
 yangguo@chromium.org