Add command to bulk set must-change-password (#22823) (#22928)

Backport #22823

As part of administration sometimes it is appropriate to forcibly tell
users to update their passwords.

This PR creates a new command `gitea admin user must-change-password`
which will set the `MustChangePassword` flag on the provided users.
---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Jason Song <i@wolfogre.com>

cmd/admin_user.go

@@ -0,0 +1,21 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package cmd
+
+import (
+	"github.com/urfave/cli"
+)
+
+var subcmdUser = cli.Command{
+	Name:  "user",
+	Usage: "Modify users",
+	Subcommands: []cli.Command{
+		microcmdUserCreate,
+		microcmdUserList,
+		microcmdUserChangePassword,
+		microcmdUserDelete,
+		microcmdUserGenerateAccessToken,
+		microcmdUserMustChangePassword,
+	},
+}