feat: add optional pprof debug endpoint

Fixes #359. This adds the pprof listening endpoint when configured.
The option requires providing the listening port. Once enabled,
pprof debug utilities are provided at this endpoint.

For example, adding to following option:
--pprof 127.0.0.1:9999
Creates a listener on localhost port 9999. You can then point a
browser to http://localhost:9999/debug/pprof/ to get access
to the debug utilities.

Another useful case is to get goroutine stack traces live with
the following:
curl 'http://localhost:9999/debug/pprof/goroutine?debug=1'

cmd/versitygw/main.go

@@ -19,6 +19,8 @@ import (
 	"crypto/tls"
 	"fmt"
 	"log"
+	"net/http"
+	_ "net/http/pprof"
 	"os"
 
 	"github.com/gofiber/fiber/v2"
@@ -44,6 +46,7 @@ var (
 	accessLog                              string
 	healthPath                             string
 	debug                                  bool
+	pprof                                  string
 	quiet                                  bool
 	iamDir                                 string
 	ldapURL, ldapBindDN, ldapPassword      string
@@ -187,6 +190,12 @@ func initFlags() []cli.Flag {
 			EnvVars:     []string{"VGW_DEBUG"},
 			Destination: &debug,
 		},
+		&cli.StringFlag{
+			Name:        "pprof",
+			Usage:       "enable pprof debug on specified port",
+			EnvVars:     []string{"VGW_PPROF"},
+			Destination: &pprof,
+		},
 		&cli.BoolFlag{
 			Name:        "quiet",
 			Usage:       "silence stdout request logging output",
@@ -373,6 +382,14 @@ func runGateway(ctx context.Context, be backend.Backend) error {
 		return fmt.Errorf("root user access and secret key must be provided")
 	}
 
+	if pprof != "" {
+		// listen on specified port for pprof debug
+		// point browser to http://<ip:port>/debug/pprof/
+		go func() {
+			log.Fatal(http.ListenAndServe(pprof, nil))
+		}()
+	}
+
 	app := fiber.New(fiber.Config{
 		AppName:           "versitygw",
 		ServerHeader:      "VERSITYGW",