[NTP Journeys] Record actionable element clicks

Adds a metric that tracks for each layout which UI elements were
clicked. The available UI elements at this time are: visits,
suggestions, and the ShowAll button.

Bug: 1414470
Change-Id: I61b06e398038acc62007673a9d8aef2d2e536deb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4344089


Commit-Queue: Roman Arora <romanarora@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118948}