Lock feed.public and feed.http-hooks config options
Summary:
Ref T6817. Ref T5726. These both bypass policy checks, and would allow an attacker who gains control of an administrative account to enable public feed, then view feed stories they could not normally see; or enable feed.http-hooks, then read the posted text.
In the longer term I'd like to remove feed.public completely (possibly providing API alternatives, if necessary).
Test Plan: Looked at options in web UI and saw them locked.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D11046