[FedCM] Implement intrusion mitigation via cooldown finch experiment 1/2

To mitigate the intrusion issue, this patch increases the current
cooldown period via a Finch experiment to make sure the changes do not
negatively impact other successful metrics.

A follow up patch will add another experiment to improve the cooldown
logic.

Bug: 398888508
Change-Id: Ia59e20f6699773d0a2b11fe58bb4e8319a7f0b62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6297528
Reviewed-by: Thomas Nguyen <tungnh@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1426251}