* Update util.go
Fix garbled/mojibake text display issues for non-English Unicode characters in browsers.
* add Content-Disposition, help handle file name on download
Author: awkj <hzzbiu@gmail.com>
* feat: add Prometheus metrics
* setup metrics using Prometheus client under /metrics endpoint
* add configuration value for metrics
* configure Prometheus middleware for generic metrics
* provide metrics for totals of users, gists and SSH keys
* modify test request to optionally return the response
* provide integration test for Prometheus metrics
* update documentation
* chore: make fmt
