[iOS] Add gambard as ios/c/b/ui OWNER

This CL adds gambard as OWNER for ios/chrome/browser/ui.
I have contributed to multiple refactoring and features work in the
directory.

Bug: None
Change-Id: I0bc3c723cae43c6ab5be80db566d43062ea0b9ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380284Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802651}

ios/chrome/browser/ui/OWNERS

@@ -3,6 +3,7 @@
 # like it needs extra review, or is related to the Omnibox.
 marq@chromium.org
 rohitrao@chromium.org
+gambard@chromium.org
 
 # Only for adding and removing flags.
 per-file ui_feature_flags.*=*