Implement Tracing and Stats

[deepakmohanakrishnan07]

Hi @pauljamescleary Do you think it would be good idea to do instrumentation using OpenCensus tracing technique. I like https://github.com/census-ecosystem/opencensus-scala has support for http4s and doobie which are used in this project.

We can start with opencensus' io.opencensus.exporter.trace.logging.LoggingTraceExporter in the beginning, and think about the tracing backend later (I think it's pluggable in opencensus).