Parse ProfileId from PlusAddress API responses

The APIs already expose the ProfileId, but the client currently ignores
it. This CL parses the ID from the received JSON and passes it on to
PlusAddressService::SavePlusAddress(). This fixes a sync-related TODO in
that function.

Bug: b/322147254
Change-Id: I44279c1f51c7ea3e677c8bdef5af9a52a9b33a55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412678


Reviewed-by: Jan Keitel <jkeitel@google.com>
Commit-Queue: Florian Leimgruber <fleimgruber@google.com>
Cr-Commit-Position: refs/heads/main@{#1281800}