Add OWNERS for docs/images/.
Add OWNERS for docs/images/.

A CL recently bounced the owners check because it adds an image for
metrics-results-ui.md:
https://codereview.chromium.org/2685703002

This CL adds a per-file ownership for docs/images/metrics-results-ui-* to mirror
the ownership for docs/metrics-results-ui.md itself.

Review-Url: https://codereview.chromium.org/2695903002

benschmaus/catapult,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult,benschmaus/catapult