update run cli command to run pipelines without an input #2203

I have a pipeline that does not take an input that I would like to run using the cli, but an input location is required (https://github.com/aboutcode-org/scancode.io/blob/main/scanpipe/management/commands/run.py#L51)

As a workaround, I can run my pipeline by using python manage.py run <pipeline> "".