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/main.go

@@ -112,35 +112,36 @@ func NewMainApp(appVer AppVersion) *cli.Command {
 			Usage:     "Set custom path (defaults to '{WorkPath}/custom')",
 		},
 	}
+	webCmd := newWebCommand()
 	// these sub-commands need to use a config file
 	subCmdWithConfig := []*cli.Command{
-		CmdWeb,
-		CmdServ,
-		CmdHook,
-		CmdKeys,
-		CmdDump,
-		CmdAdmin,
-		CmdMigrate,
-		CmdDoctor,
-		CmdManager,
-		CmdEmbedded,
-		CmdMigrateStorage,
-		CmdDumpRepository,
-		CmdRestoreRepository,
-		CmdActions,
+		webCmd,
+		newServCommand(),
+		newHookCommand(),
+		NewKeysCommand(),
+		newDumpCommand(),
+		newAdminCommand(),
+		newMigrateCommand(),
+		newDoctorCommand(),
+		newManagerCommand(),
+		newEmbeddedCommand(),
+		newMigrateStorageCommand(),
+		newDumpRepositoryCommand(),
+		newRestoreRepositoryCommand(),
+		newActionsCommand(),
 	}
 
 	// these sub-commands do not need the config file, and they do not depend on any path or environment variable.
 	subCmdStandalone := []*cli.Command{
 		cmdConfig(),
 		cmdCert(),
-		CmdGenerate,
-		CmdDocs,
+		newGenerateCommand(),
+		newDocsCommand(),
 	}
 
 	// TODO: we should eventually drop the default command,
 	// but not sure whether it would break Windows users who used to double-click the EXE to run.
-	app.DefaultCommand = CmdWeb.Name
+	app.DefaultCommand = webCmd.Name
 
 	app.Before = PrepareConsoleLoggerLevel(log.INFO)
 	for i := range subCmdWithConfig {