feat(pprof): add pprof HTTP server (#807)

- `PPROF_ENABLED=no`
- `PPROF_BLOCK_PROFILE_RATE=0`
- `PPROF_MUTEX_PROFILE_RATE=0`
- `PPROF_HTTP_SERVER_ADDRESS=":6060"`

internal/httpserver/logger.go

@@ -0,0 +1,9 @@
+package httpserver
+
+// Logger is the logger interface accepted by the
+// HTTP server.
+type Logger interface {
+	Info(msg string)
+	Warn(msg string)
+	Error(msg string)
+}