feat: ability to specify cli flags via env variables

pkg/command/command.go

@@ -48,34 +48,40 @@ func Run() error {
 			Aliases:     []string{"web.listen-address"},
 			Value:       "0.0.0.0:9176",
 			Usage:       "Address to bind the metrics server",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_WEB_ADDRESS"},
 			Destination: &cfg.Server.Addr,
 		},
 		&cli.StringFlag{
 			Name:        "web.path",
 			Aliases:     []string{"web.telemetry-path"},
 			Value:       "/metrics",
 			Usage:       "Path to bind the metrics server",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_WEB_PATH"},
 			Destination: &cfg.Server.Path,
 		},
 		&cli.StringFlag{
 			Name:        "web.root",
 			Value:       "/",
 			Usage:       "Root path to exporter endpoints",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_WEB_ROOT"},
 			Destination: &cfg.Server.Root,
 		},
 		&cli.StringSliceFlag{
 			Name:     "status-file",
 			Usage:    "The OpenVPN status file(s) to export (example test:./example/version1.status )",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_STATUS_FILE"},
 			Required: true,
 		},
 		&cli.BoolFlag{
 			Name:  "disable-client-metrics",
 			Usage: "Disables per client (bytes_received, bytes_sent, connected_since) metrics",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_DISABLE_CLIENT_METRICS"},
 		},
 		&cli.BoolFlag{
 			Name:        "enable-golang-metrics",
 			Value:       false,
 			Usage:       "Enables golang and process metrics for the exporter) ",
+			EnvVars: 	 []string{"OPENVPN_EXPORTER_ENABLE_GOLANG_METRICS"},
 			Destination: &cfg.ExportGoMetrics,
 		},
 	}