R1:3df1e175273f

Add a side nav to Conduit API method console pages

Summary: Ref T13072. Make large Conduit doc pages a bit more navigable. This prepares for updating "harbormaster.sendmessage" to support sending messages to builds.

Test Plan: Viewed various Conduit API documentation pages, clicked links.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13072

Differential Revision: https://secure.phabricator.com/D21696