PLT-3077 Add group messaging (#5489)

* Implement server changes for group messaging

* Majority of client-side implementation

* Some server updates

* Added new React multiselect component

* Fix style issues

* Add custom renderer for options

* Fix model test

* Update ENTER functionality for multiselect control

* Remove buttons from multiselect UI control

* Updating group messaging UI (#5524)

* Move filter controls up a component level

* Scroll with arrow keys

* Updating mobile layout for multiselect (#5534)

* Fix race condition when backspacing quickly

* Hidden or new GMs show up for regular messages

* Add overriding of number remaining text

* Add UI filtering for team if config setting set

* Add icon to channel switcher and class prop to status icon

* Minor updates per feedback

* Improving group messaging UI (#5563)

* UX changes per feedback

* Update email for group messages

* UI fixes for group messaging (#5587)

* Fix missing localization string

* Add maximum users message when adding members to GM

* Fix input clearing on Android

* Updating group messaging UI (#5603)

* Updating UI for group messaging (#5604)

model/websocket_message.go

@@ -16,6 +16,7 @@ const (
 	WEBSOCKET_EVENT_CHANNEL_DELETED    = "channel_deleted"
 	WEBSOCKET_EVENT_CHANNEL_CREATED    = "channel_created"
 	WEBSOCKET_EVENT_DIRECT_ADDED       = "direct_added"
+	WEBSOCKET_EVENT_GROUP_ADDED        = "group_added"
 	WEBSOCKET_EVENT_NEW_USER           = "new_user"
 	WEBSOCKET_EVENT_LEAVE_TEAM         = "leave_team"
 	WEBSOCKET_EVENT_UPDATE_TEAM        = "update_team"