Fix listen address and port passing

Only HOST & PORT env variables used by gin internally were really used, pass resulting config to gin so we match documentation, and log it on startup

docs/example.yaml

@@ -25,7 +25,7 @@ labels:
   keep: []
   strip: []
 listen:
-  address: "*"
+  address: "0.0.0.0"
   port: 8080
   prefix: /
 log:

internal/config/config.go

@@ -62,7 +62,7 @@ func init() {
 	pflag.StringSlice("receivers.strip", []string{},
 		"List of receivers to not display alerts for")
 
-	pflag.String("listen.address", "*", "IP/Hostname to listen on")
+	pflag.String("listen.address", "", "IP/Hostname to listen on")
 	pflag.Int("listen.port", 8080, "HTTP port to listen on")
 	pflag.String("listen.prefix", "/", "URL prefix")
 

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"html/template"
 	"path"
 	"strings"
@@ -150,7 +151,9 @@ func main() {
 	}
 
 	setupRouter(router)
-	err := router.Run()
+	listen := fmt.Sprintf("%s:%d", config.Config.Listen.Address, config.Config.Listen.Port)
+	log.Infof("Listening on %s", listen)
+	err := router.Run(listen)
 	if err != nil {
 		log.Fatal(err)
 	}