heap: Add Oilpan folks to OWNERS

Bug: chromium:1056170
Change-Id: Id7859be3e28331a78dd548b445272cc645ce50d1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2116202Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66845}

src/heap/OWNERS

+bikineev@chromium.org
 dinfuehr@chromium.org
 hpayer@chromium.org
 mlippautz@chromium.org
+omerkatz@chromium.org
 ulan@chromium.org
 
 per-file *factory*=leszeks@chromium.org