Cross platform background process launching

[danieljurek]

Using Start-Process works well enough on Windows but it's not working properly in Linux (even Start-Process nohup -Arguments @('arg1, ...))... There should be a way to do this so that the task teardown doesn't stop the running process. Running nohup from a bash shell works, why not pwsh?

The issue that brought this forth came from this PR where I suggested something that might've worked but did not work when tested: https://github.com/Azure/azure-sdk-for-cpp/pull/3823/files