Proxy VCS SSH requests

Summary: Fixes T7034. Like HTTP, proxy requests to the correct host if a repository has an Almanac service host.

Test Plan: Ran VCS requests through the proxy.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7034

Differential Revision: https://secure.phabricator.com/D11543