Improve consistency in use of "via", "objectPHID", and "containerPHID" parameters in repository workers

Summary:
Ref T13591. Improve how parameters are passed between commit worker tasks:

• Always pass "via", to track where tasks came from.
• Always provide "objectPHID" (with the commit PHID).
• Always provide "containerPHID" (with the repository PHID).

Test Plan:

• Pushed a new commit.
• Ran bin/repository pull + bin/repository discover, saw commit with all parameters.
• Ran bin/worker execute ..., saw a Change worker and then a Publish worker with appropriate parameters.
• Ran bin/repository reparse ... --background, saw workers queue with appropriate parameters.

Maniphest Tasks: T13591

Differential Revision: https://secure.phabricator.com/D21532