Add OWNERS for sdk extensions version updates

Our team performs the mainline sdk releases and has to update the sdk
extensions version on every release.

Adding people who are involved in the sdk ext release process so that
changes related to sdk extensions version updates can be approved by
our team.

We will only be approving changes which updates sdk extensions version.

Bug: N/A
Test: N/A
Change-Id: I42755dbae7054161f56e789b57e064084eebc7c7