Support opt-in events in SB private event router

These events are a different type of reporting connector event. Instead
of being enabled by default, the admin has to explicitly enable them and
specify a list of URL patterns that the event must match to be reported.

Bug: 1238577
Change-Id: If0c49913e00b8d15d33e251cf0f914b8e609f543
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3440554
Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Reviewed-by: Marc-André Decoste <mad@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Anthony Vallée-Dubois <anthonyvd@chromium.org>
Cr-Commit-Position: refs/heads/main@{#968701}