Add a ServiceProfiler mode to collect traces

Summary: Ref T13106. This is a little awkward (the traces are blobs of text in a denormalized format with redundant library version information) but better than nothing.

Test Plan: In a future change, made "Analyze Query Plans" enable stack trace mode. Collected and rendered stack traces.

Maniphest Tasks: T13106

Differential Revision: https://secure.phabricator.com/D19220