feat(release): generate the GitHub release body from the changelog (#2987)

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

cmd/release/main.go

@@ -43,20 +43,29 @@ var changelogReleaseRegex = regexp.MustCompile(`## Unreleased`)
 // Flags
 var (
 	versionFlag bool
+	notesFlag   bool
 )
 
 func init() {
 	pflag.BoolVarP(&versionFlag, "version", "v", false, "resolved version number")
+	pflag.BoolVar(&notesFlag, "notes", false, "changelog section of the current version, for the GitHub release body")
 	pflag.Parse()
 }
 
 func main() {
-	if err := release(); err != nil {
+	if err := run(); err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
 }
 
+func run() error {
+	if notesFlag {
+		return notes(os.Stdout)
+	}
+	return release()
+}
+
 func release() error {
 	if len(pflag.Args()) != 1 {
 		return errors.New("error: expected version number")