[Product specifications] Add enterprise policy

This patch adds the declaration for the enterprise policy for product
specifications. The policy is not checked anywhere yet, but is needed
for network annotation definitions in subsequent patches.

Bug: b:325109916
Change-Id: If3191068904cbf22449183db63d463d1426be2d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5297236


Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Sébastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1265934}