Add OWNERS for VTS module VtsHalGraphicsComposerV2_1TargetTest

Each VTS module is required to have OWNERS file. The ownership is based on
go/vts-owners. For more information about ownership policy, please visit
go/xts-owners-policy.

Test: Tree Hugger
Bug: 143903671
Change-Id: I6647af3a0af6cb707904a454eef78c6c509035ec