Add access policy

Adds the access policy, based on content from https://wikimedia.org/api/rest_v1/#/

Regarding rate limits, based on https://phabricator.wikimedia.org/T341569, it seems that rate limited may not be implemented in the REST gateway currently. In order to avoid potential blockers, I've kept the original rate limits from the RESTBase docs in a giant, per-endpoint table. We can always change this later if simpler rate limits are decided on.

Bug: T364799