feat: metrics collection & tracking

[xendarboh]

• use and evaluate current og trellis metrics system (see res.json and pprof)
• record metrics to db (not flat files...)
• track changes over time with particular interest in:
  • correlating effects of mix-net parameters on data transmission characteristics
  • correlating code and component evolution to performance
• R&D proof-of-network characteristics of individual servers as it relates to their mix-net round qualifications