Move the top level variables in phabricator role in a class

Introduce the role::phabricator::config class that houses the various
configuration variables used throughout phabricator. Update the role
manifests that use those. That way, those variables do not pollute the
top scope and unconditional inclusion of passwords::mysql::phabricator
in the top scope stops

Bug: T78344
Change-Id: Ie50c4ee26b5f6627c571d98f0d9ad1ed7ed3911b
Merge "Move the top level variables in phabricator role in a class" into production