[iOS][Credential-Provider] Add OWNERS file.

Bug: 1045456
Change-Id: Ibf91aff0fef477255751a689692be281d098ceba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2119530
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753800}

ios/chrome/common/credential_provider/OWNERS

+javierrobles@chromium.org
+djean@chromium.org
+
+# TEAM: ios-directory-owners@chromium.org
+# OS: iOS