Provision Etherpad API key to Wolfplex datastore

Summary:
Wolfplex API needs Etherpad API key to get the list of pads.

approved-by: Wolfplex blanket approval for servers management

Test Plan: Browse https://api.wolfplex.org/pads/

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2821