Don't reset session on change_type

[axelson]

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From looking at the code (and experimenting) it appears that when you have a change_type in your configuration, a new session is generated (unless there is one to restore from): https://github.com/processone/tsung/blob/4094df6054727f39fc45f999d719433f0047a5a8/src/tsung/ts_client.erl#L488

Instead I'd like to be able to keep the session that was previously being used. My use-case is that I am trying to do load testing of Phoenix LiveView and I need to keep the session from an HTTP request to a Websocket request. Is it possible to add such a configuration option?