Make the success message from "bin/config" more clear

Summary:
Ref T13373. When you "bin/config set x ..." a value, the success message ("Set x ...") is somewhat ambiguous and can be interpreted as "First, you need to set x..." rather than "Success, wrote x...".

Make the messaging more explicit. Also make this string more translatable.

Test Plan: Ran bin/config set ... with various combinations of flags, saw more clear messaging.

Maniphest Tasks: T13373

Differential Revision: https://secure.phabricator.com/D20711