MM-60987: Move message_export code to monorepo (#28674)

* move message_export code to monorepo

* update license headers

* moving over `dedicated filestore` (#1772) from enterprise master

server/enterprise/message_export/main_test.go

@@ -0,0 +1,21 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.enterprise for license information.
+
+package message_export
+
+import (
+	"testing"
+
+	"github.com/mattermost/mattermost/server/v8/channels/api4"
+	"github.com/mattermost/mattermost/server/v8/channels/testlib"
+)
+
+var mainHelper *testlib.MainHelper
+
+func TestMain(m *testing.M) {
+	mainHelper = testlib.NewMainHelper()
+	defer mainHelper.Close()
+	api4.SetMainHelper(mainHelper)
+
+	mainHelper.Main(m)
+}