tor-guardmgr: Add vanguards API skeleton.
This MR
- adds an initial API for the vanguard manager. Note this only partially addresses #1275 (closed) (the design described in the ticket includes some functions I haven't added yet). The vanguards API is behind an experimental
vanguards
feature because its shape is not final - gives
CircMgr
a handle toVanguardMgr
(closes #1277 (closed)) - adds a tentative
VanguardConfig
andVanguardParams
for configuring vanguards (I'm not sure we need bothVanguardConfig
andVanguardParams
, so we might end up unifying these later down the line) - adds the
VanguardConfig
toTorClientConfig
, and sprinklesreconfigure
calls throughout the code for handlingVanguardConfig
changes