Currently, python scripts can import [`paraview.web.venv`](https://gitlab.kitware.com/paraview/paraview/-/blob/master/Web/Python/paraview/web/venv.py) to setup module paths etc. to load packages from a virualenv. The current approach requires that `import paraview.web.venv` is done in the Python script that pvpython/pvbatch executes, which makes it impossible for the Python script itself to be a part of the virtual env. For example, I have a nice Python package with Viz pipelines that I pip install in a venv. I simply want to run that package with pvpython as follows: ```sh pvpython -m my_nice_package ``` It's not possible currently. Hence, I propose we move the venv handling to pvpython/pvbatch itself. Thus, make the following work: ```sh pvpython --venv /.../venv -m my_nice_package ``` It makes sense to add this cmd-line arg to all executables that support Python including the server executables.