Suspicion: Servicehub + devenv might not terminate upon close + improve temp file cleaning

**System Information (please complete the following information):**
Latest updates as of 11.7.2021, VS 161.0.3, Windows Server 2019

**Describe the bug**
AppData/Temp folder can quickly get big especially after failed training attempts.
It might be a good idea to remind users to clean it, or perhaps have Model builder check and ask if it should be cleaned.

I am also suspecting some parts of model builder may still keep running under some circumstances after closing Visual studio, even if did not fully crash (I am not sure if I received any errors during this session).
_Visual Studio was closed when these processes kept running, other users were also signed off from the server_

This still needs to be confirmed, but it could explain https://github.com/dotnet/machinelearning-modelbuilder/issues/1535

This is more as a FYI of the suspicion, and I think it could be said user is responsible for clearing temp folders. Feel free to close or keep open.