Adding OWNERS file for osx_sdk recipe module

Updating the OWNERS for osx sdk packages. List suggested from
crrev/c/2422449.

Change-Id: Id582737a539d8c10ec3437994068c33dd8c6d46a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2424556
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Gary Tong <gatong@chromium.org>

recipes/recipe_modules/osx_sdk/OWNERS

+jeffyoon@google.com
+lindsayw@google.com
+
+# Backup
+gatong@google.com
+martiniss@google.com
+estaab@google.com
+gbeaty@google.com