Add private metric report encryption

Implement functionality to fetch public key and encrypt private metrics
report for DWA.

from third_party protocol buffer dependencies.
NO_IFTTT=dwa_egtest.mm will add support for PrivateMetricsFeature in a
separate CL.

Bug: 411369489
Change-Id: Ib4a1baae22064b4c7e8d9897ae8de979f2aef6f7
Binary-Size: Size increase is unavoidable because increase is largely
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6913363
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Jay Zhou <zhouzj@google.com>
Cr-Commit-Position: refs/heads/main@{#1515492}
NOKEYCHECK=True
GitOrigin-RevId: cbc6209a5a8eb373d40b1b8f3cd461b8be9a621b