Add push and pull handlers

[Gitii]

Hi @licanhua,

This PR adds two new handlers:

• Pull File
• Push File

All clients should happily use these routes and work out of the box.

I also upgraded all dependencies and .net version to 6.0 because .net core 3.1 is eol.
I also added e2e tests for both handlers which cover the happy path and error cases.

Beside that I have noticed that tests based on notepad.exe fail because the "remastered" notepad for windows 11 has a multi-process design (i think). The session creation fails because the created process is not the one with the ui. Pretty tricky use case. winver works as expected.

I would be great if you could review my PR and give feedback.

[Gitii]

@licanhua I recommend creating a publish profile with a standalone configuration (framework independent build to avoid a .net 6 runtime dependency). I haven't found any documentation of the deployment process and therefore decided to let you decide.

[licanhua]

@Gitii Thanks for your contribution. I published a release for your PR