Flip feature flag for KerberosInBrowser feature

This feature is planned to launch in M-116.
Launch bug: https://launch.corp.google.com/launch/4210638

Bug: b:260522530
Change-Id: I05971e26b4fd65786a65445b85c5347bfef129a8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4563294


Reviewed-by: Felipe Andrade <fsandrade@chromium.org>
Commit-Queue: Michael Slutskii <slutskii@google.com>
Commit-Queue: David Benjamin <davidben@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Auto-Submit: Michael Slutskii <slutskii@google.com>
Cr-Commit-Position: refs/heads/main@{#1148625}