PLT-7622 Improvements to server handling of webapp plugins (#7445)

* Improvements to server handling of webapp plugins

* Fix newline

* Update manifest function names

model/websocket_message.go

@@ -39,6 +39,8 @@ const (
 	WEBSOCKET_EVENT_RESPONSE            = "response"
 	WEBSOCKET_EVENT_EMOJI_ADDED         = "emoji_added"
 	WEBSOCKET_EVENT_CHANNEL_VIEWED      = "channel_viewed"
+	WEBSOCKET_EVENT_PLUGIN_ACTIVATED    = "plugin_activated"   // EXPERIMENTAL - SUBJECT TO CHANGE
+	WEBSOCKET_EVENT_PLUGIN_DEACTIVATED  = "plugin_deactivated" // EXPERIMENTAL - SUBJECT TO CHANGE
 )
 
 type WebSocketMessage interface {