Add "bin/worker delay" and "bin/worker priority" utilities for managing task queues

Summary: Ref T13591. Support delaying selected tasks until a later time and bulk-adjustment of task priority.

Test Plan: Ran bin/worker delay and bin/worker priority to delay and reprioritize tasks. Confirmed outcomes with daemon console.

Maniphest Tasks: T13591

Differential Revision: https://secure.phabricator.com/D21535