MM-10254 Add plugin APIs for getting/updating user statuses (#9101)

* Add plugin APIs for getting/updating user statuses

* Add and update tests

* Updates per feedback

api4/websocket_test.go

@@ -404,7 +404,7 @@ func TestWebSocketStatuses(t *testing.T) {
 	time.Sleep(1500 * time.Millisecond)
 
 	th.App.SetStatusAwayIfNeeded(th.BasicUser.Id, false)
-	th.App.SetStatusOnline(th.BasicUser.Id, "junk", false)
+	th.App.SetStatusOnline(th.BasicUser.Id, false)
 
 	time.Sleep(1500 * time.Millisecond)