Test for websocket ping on the creation of the resource which has been subscribed to

[timbl]

in https://github.com/solid/test-suite/blob/master/testers/websockets-pubsub/tester/test/surface/change-events.test.ts let us have also another test just the same except the subscription is to the resource which is created, not the container.

ie a test with

   wsClient.send('sub http://server:8080/asdf/')

replaced with

   wsClient.send('sub http://server:8080/asdf/test.txt')

see also https://github.com/solid/solid-spec/issues/217