Add a bin/conduit call support binary

Summary:
Ref T13060. See PHI343. Triaging this bug required figuring out where in the pipeline UTF8 was being dropped, and bisecting the pipeline required making calls to Conduit.

Currently, there's no easy way to debug/inspect arbitrary Conduit calls, especially when they are diffusion.* calls which route to a different host (even if you have a real session and use the web console for these, you just see an HTTP service call to the target host in DarkConsole).

Add a bin/conduit utility to make this kind of debugging easier, with an eye toward the Phacility production cluster (or other similar clusters) specifically.

Test Plan:

• Ran echo '{}' | bin/conduit call --method conduit.ping --input - and similar.
• Used a similar approach to successfully diagnose the UTF8 issue in T13060.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13060

Differential Revision: https://secure.phabricator.com/D18987