Add `metricsPrivate.recordExtensionUsageUkm` API to record extension usage UKM events.

Bug: 432507393
Change-Id: I20b223e70732907093a11263bd6a07017cb77599
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7148743
Reviewed-by: Chad Duffin <chadduffin@chromium.org>
Reviewed-by: Justin Lulejian <jlulejian@chromium.org>
Commit-Queue: marissa shen <marissashen@google.com>
Cr-Commit-Position: refs/heads/main@{#1549413}
NOKEYCHECK=True
GitOrigin-RevId: e9a99b5832de1817d0af643d0189822f63ebfd3f