Parameterize PhabricatorGlobalLock

Summary:
Ref T13096. Currently, we do a fair amount of clever digesting and string manipulation to build lock names which are less than 64 characters long while still being reasonably readable.

Instead, do more of this automatically. This will let lock acquisition become simpler and make it more possible to build a useful lock log.

Test Plan: Ran bin/repository update, saw a reasonable lock acquire and release.

Maniphest Tasks: T13096

Differential Revision: https://secure.phabricator.com/D19173