Add zip cli command, generate requirements.txt during scan, and add example jupyter notebook

[markdlv-sf]

• Users can now run datacustomcode zip or datacustomcode zip payload to zip up their package for deployment. This is needed because our UI expects you to have a zip ready, and we want customers using docker to build their zips to avoid platform/architecture mismatches between their machines and DataCloud compute
• When running datacustomcode scan ./payload/entrypoint.py, requirement.txt is also updated. This catches a scenario where you've pip installed into the venv you're working in, but forgotten to add it to requirements.txt (which drives our zip process).
• Added jupyter notebook example to provide a better starting point once jupyter lab is started

[salesforce-cla]

Thanks for the contribution! It looks like @chandresh-patelsf is an internal user so signing the CLA is not required. However, we need to confirm this.

[sbyrne-sf]

looks good to me.