Split web server into separate package

[josephmckinsey]

• Eliminated npm part in setup.py commands
• Created separate package
• rename to helics_cli_extras
• move observer stuff to helics_cli_extras
• move testing if necessary
• setup ci
• setup cd and PyPI package (🤞)
• Changed CI to run on push to main or pull request to main (prevents annoying duplication)

[nightlark]

Relates to #86

For configuring the CI/CD workflow for this with PyPI publishing, use:

Repository: [GMLC-TDC/pyhelics](https://github.com/GMLC-TDC/pyhelics)
Workflow: cd-cli-extras.yml
Environment name:        pypi-cli-extras

[nightlark]

For backlog to make sdist eventually work: a custom in-source tree build backend interface that runs npm commands would likely be what we want.

[josephmckinsey]

P.S. I had to remove the python package "install" that was being added to our python dependencies in the github actions workflow. I believe it was never intended to be installed.

[nightlark]

It looks so much nicer not having all that code just to run npm in the setup.py -- only thing I'm not sure about is if we should have checks for those two imports to return a nicer error message if a user tries to run those functions without installing the helics-cli-extras.

[nightlark]

I think the workflow changes look okay -- after merging try triggering the workflow to publish an initial version of the helics-cli-extras package.