MM-12843 Add interactive dialogs (#9816)

* Add interactive dialogs

* Fix unit test

* Updates per feedback

* Fix typo

* Updates per feedback, add icon_url and error returns

* Updates per feedback

* Update per feedback

api4/api.go

@@ -231,6 +231,7 @@ func Init(a *app.App, root *mux.Router) *API {
 	api.InitScheme()
 	api.InitImage()
 	api.InitTermsOfService()
+	api.InitAction()
 
 	root.Handle("/api/v4/{anything:.*}", http.HandlerFunc(api.Handle404))