Feed - permenantly fail publish workers if the uri they are posting to is not in configu

Summary: Fixes T5958

Test Plan: i just used the ole logic noodle on this one

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5958

Differential Revision: https://secure.phabricator.com/D10359