[ios] Add OWNERS for //ios/c/b/ui/commands

We need OWNERS for the commands folder, especially as they are actively
being refactored.

Change-Id: I106373a92ea59db68514546d5315a5e4110610a9
Reviewed-on: https://chromium-review.googlesource.com/c/1354495
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612225}

ios/chrome/browser/ui/commands/OWNERS

+edchin@chromium.org
+gambard@chromium.org
+marq@chromium.org
+rohitrao@chromium.org
+
+# TEAM: ios-directory-owners@chromium.org
+# OS: iOS