chore: set User-Agent on all outgoing HTTP requests (#10867)

It's only polite, and it enables better troubleshooting in situations
like weird-ass requests to the upgrades download service.

---------

Signed-off-by: Jakob Borg <jakob@kastelo.net>

lib/upgrade/upgrade_supported.go

@@ -15,20 +15,19 @@ import (
 	"compress/gzip"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
 	"os"
 	"path"
 	"path/filepath"
-	"runtime"
 	"sort"
 	"strings"
 	"time"
 
 	"github.com/shirou/gopsutil/v4/host"
 	"github.com/syncthing/syncthing/internal/slogutil"
+	"github.com/syncthing/syncthing/lib/build"
 	"github.com/syncthing/syncthing/lib/dialer"
 	"github.com/syncthing/syncthing/lib/signature"
 	"github.com/syncthing/syncthing/lib/tlsutil"
@@ -79,13 +78,13 @@ func init() {
 	osVersion = strings.TrimSpace(osVersion)
 }
 
-func upgradeClientGet(url, version string) (*http.Response, error) {
+func upgradeClientGet(url string) (*http.Response, error) {
 	req, err := http.NewRequest(http.MethodGet, url, nil)
 	if err != nil {
 		return nil, err
 	}
 
-	req.Header.Set("User-Agent", fmt.Sprintf(`syncthing %s (%s %s-%s)`, version, runtime.Version(), runtime.GOOS, runtime.GOARCH))
+	req.Header.Set("User-Agent", build.UserAgent())
 	if osVersion != "" {
 		req.Header.Set("Syncthing-Os-Version", osVersion)
 	}
@@ -95,7 +94,7 @@ func upgradeClientGet(url, version string) (*http.Response, error) {
 // FetchLatestReleases returns the latest releases. The "current" parameter
 // is used for setting the User-Agent only.
 func FetchLatestReleases(releasesURL, current string) []Release {
-	resp, err := upgradeClientGet(releasesURL, current)
+	resp, err := upgradeClientGet(releasesURL)
 	if err != nil {
 		slog.Warn("Failed to fetch latest release information", slogutil.Error(err))
 		return nil
@@ -227,6 +226,7 @@ func readRelease(archiveName, dir, url string) (string, error) {
 	}
 
 	req.Header.Add("Accept", "application/octet-stream")
+	req.Header.Set("User-Agent", build.UserAgent())
 	resp, err := upgradeClient.Do(req)
 	if err != nil {
 		return "", err