Switch cmd/ to use constructor functions. (#36962)

This is a step towards potentially splitting command groups into their
own folders to clean up `cmd/` as one folder for all cli commands.
Returning fresh command instances will also aid in adding tests as you
don't need to concern yourself with the whole command tree being one
mutable variable.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

cmd/admin.go

@@ -18,36 +18,41 @@ import (
 	"github.com/urfave/cli/v3"
 )
 
-var (
-	// CmdAdmin represents the available admin sub-command.
-	CmdAdmin = &cli.Command{
+func newAdminCommand() *cli.Command {
+	return &cli.Command{
 		Name:  "admin",
 		Usage: "Perform common administrative operations",
 		Commands: []*cli.Command{
-			subcmdUser,
-			subcmdRepoSyncReleases,
-			subcmdRegenerate,
-			subcmdAuth,
-			subcmdSendMail,
+			newUserCommand(),
+			newRepoSyncReleasesCommand(),
+			newRegenerateCommand(),
+			newAuthCommand(),
+			newSendMailCommand(),
 		},
 	}
+}
 
-	subcmdRepoSyncReleases = &cli.Command{
+func newRepoSyncReleasesCommand() *cli.Command {
+	return &cli.Command{
 		Name:   "repo-sync-releases",
 		Usage:  "Synchronize repository releases with tags",
 		Action: runRepoSyncReleases,
 	}
+}
 
-	subcmdRegenerate = &cli.Command{
+func newRegenerateCommand() *cli.Command {
+	return &cli.Command{
 		Name:  "regenerate",
 		Usage: "Regenerate specific files",
 		Commands: []*cli.Command{
-			microcmdRegenHooks,
-			microcmdRegenKeys,
+			newRegenerateHooksCommand(),
+			newRegenerateKeysCommand(),
 		},
 	}
+}
 
-	subcmdAuth = &cli.Command{
+func newAuthCommand() *cli.Command {
+	return &cli.Command{
 		Name:  "auth",
 		Usage: "Modify external auth providers",
 		Commands: []*cli.Command{
@@ -59,12 +64,14 @@ var (
 			microcmdAuthUpdateLdapSimpleAuth(),
 			microcmdAuthAddSMTP(),
 			microcmdAuthUpdateSMTP(),
-			microcmdAuthList,
-			microcmdAuthDelete,
+			newAuthListCommand(),
+			newAuthDeleteCommand(),
 		},
 	}
+}
 
-	subcmdSendMail = &cli.Command{
+func newSendMailCommand() *cli.Command {
+	return &cli.Command{
 		Name:   "sendmail",
 		Usage:  "Send a message to all users",
 		Action: runSendMail,
@@ -86,7 +93,7 @@ var (
 			},
 		},
 	}
-)
+}
 
 func idFlag() *cli.Int64Flag {
 	return &cli.Int64Flag{