Investigate and document additional overhead for first hop when not using guards
Initial plots in legacy/trac#25774 (moved) have shown that there is considerably higher circuit build latency from building the 1st hop compared to subsequent hops. This may be due to not using guards and some additional overhead that is not seen by normal clients when using guards (as it happens before the circuits are actually needed).
We should investigate this and document it as part of the page on Tor Metrics for legacy/trac#25774 (moved).