module to export monitoring metrics for Prometheus

 Net::Prometheus provides the ability for a program to collect monitoring
 metrics and export them to the Prometheus.io monitoring server.
 .
 As Prometheus will expect to collect the metrics by making an HTTP request,
 facilities are provided to yield a PSGI application that the containing
 program can embed in its own structure to provide the results, or the
 application can generate a plain-text result directly and serve them by its
 own means.