[PriceInsights][iOS] PriceInsights model skeleton

Bug: b/326448363
Change-Id: I383a3be0f6f36910eb0d433fe43a010ce2dd0314
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5383888


Reviewed-by: Ayman Almadhoun <ayman@chromium.org>
Commit-Queue: Cheick Cisse <cheickcisse@google.com>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/main@{#1278876}