Add OWNERS to //blink/public/common/privacy_budget.

Given that folks have shifted around, updating the OWNERs for this code
seems reasonable. This CL adds antoniosartori@ and mkwst@, and
alphabetizes the file.

Change-Id: I613b79c3bcf085d33727aeac474bf46c30c1c814
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3563141
Auto-Submit: Mike West <mkwst@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/main@{#988387}

third_party/blink/public/common/privacy_budget/OWNERS

@@ -1,2 +1,4 @@
-pauljensen@chromium.org
+antoniosartori@chromium.org
 caraitto@chromium.org
+mkwst@chromium.org
+pauljensen@chromium.org