Can not run test with Click utility

We are currently using subprocess.check_output for testing the CLI. It does work fine.

To set-up the CI, subprocess is calling to silkaj from the shell PATH. As it is not defined in the Docker image, it does not work. For, now, I propose to call poetry run silkaj sub-cmd to by-pass next issue.

But if we want to use Click helper to test the CLI, for extra features such as tests on the terminal size, it does not work. It is due to the aiohttp session which gets closed by the first test closing the session. Then other tests get this closed session because of the singleton. It looks like Click test utility does not restart from a clean context.