all: print --help output to stdout instead of stderr

This is easier to grep and pipe

app/victoria-metrics/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"net/http"
+	"os"
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/app/vminsert"
@@ -25,6 +26,8 @@ var (
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	envflag.Parse()
 	buildinfo.Init()
 	logger.Init()

app/vmagent/main.go

@@ -4,6 +4,7 @@ import (
 	"flag"
 	"fmt"
 	"net/http"
+	"os"
 	"strings"
 	"time"
 
@@ -49,6 +50,8 @@ var (
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	envflag.Parse()
 	buildinfo.Init()
 	logger.Init()

app/vmalert/main.go

@@ -58,6 +58,8 @@ absolute path to all .yaml files in root.`)
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	envflag.Parse()
 	buildinfo.Init()
 	logger.Init()

app/vmauth/main.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"os"
 	"time"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/buildinfo"
@@ -19,6 +20,8 @@ var (
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	envflag.Parse()
 	buildinfo.Init()
 	logger.Init()

app/vmbackup/main.go

@@ -31,6 +31,8 @@ var (
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	flag.Usage = usage
 	envflag.Parse()
 	buildinfo.Init()

app/vmrestore/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"os"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/backup/actions"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/backup/common"
@@ -24,6 +25,8 @@ var (
 )
 
 func main() {
+	// Write flags and help message to stdout, since it is easier to grep or pipe.
+	flag.CommandLine.SetOutput(os.Stdout)
 	flag.Usage = usage
 	envflag.Parse()
 	buildinfo.Init()