Make "arc upload" chunk-aware

Summary: Ref T7149. This makes the client try to use the new file.allocate API before falling back to the old stuff.

Test Plan: Used arc upload to upload files. With chunking forced, uploaded chunked files.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: joshuaspence, epriestley

Maniphest Tasks: T7149

Differential Revision: https://secure.phabricator.com/D12061