MM-53125 Add feature to convert group message to private channel (#24421)

* Added convert to channel menu item

* WIP

* refactored channel name input field and created conversion modal

* style

* style

* WIP

* wip

* Created API to fetch common teams of GM members

* Added UI for all members deactivated

* Fetched common teams in client

* WIP

* Added a required attribute to DropdownInput component

* Fixed a case with dropdown input required flag

* WIP

* API first draft

* Genetayed layers and mocks

* Fixed create channel bug

* WIP

* Added cache invalidation

* Calling API from client

* Updated API to accept name and display name as well

* WIP

* Moved converted GM to correct category

* Style fixes

* Added logic to move user to new team/channel after GM conversion

* Prevented guest user from performing action

* Added loading indicator

* Added smoother height transistion when loading finishes

* UI imporvements

* WIP

* Formatted GM conversion message on client side

* lint fix

* Moved convert option from sidebar menu to channel header menu

* Some cleanup

* Updated server layers

* Fixed i18n

* Fixed types

* Fix server i18n

* Fixed channel creation bug

* Added store test for GetCommonTeamIDsForMultipleUsers

* Server tests done

* Updated snapshots

* Updated layers

* lint fix

* Update tests

* For CI

* lint

* restored debug code

* Used user ID instead of username in channel conversion post

* WIP

* Review fixes

* LInt fixes

* Test fix

* WIP

* WIP

* WIP

* wip

* Review fixes, lots of them

* Review fix

* Disabled WIP test

* test

* Cleanup

* Test fix

* removed testing line

* Fixed incorrect default message

* Review fixes

* Fixes

* lint and i18n fix

* Setting category on server side

* updated i18n

* Updated tests

* Added tests

* Refs cleanup

* added test

---------

Co-authored-by: Harshil Sharma <harshilsharma@Harshils-MacBook-Pro.local>

server/channels/utils/humanize.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package utils
+
+import (
+	"strings"
+
+	"github.com/mattermost/mattermost/server/public/shared/i18n"
+)
+
+func JoinList(items []string) string {
+	if len(items) == 0 {
+		return ""
+	} else if len(items) == 1 {
+		return items[0]
+	} else {
+		return i18n.T(
+			"humanize.list_join",
+			map[string]any{
+				"OtherItems": strings.Join(items[:len(items)-1], ", "),
+				"LastItem":   items[len(items)-1],
+			})
+	}
+}