Allow code uploads for function registration

[aFuerst]

WIP changes that allow user to specify code files on registration to upload to the control plane. The worker installs Python dependencies from an also provided reqs.txt file on registration . Both code and dependencies are then mounted into the container on boot and server will pick them up via PYTHONPATH.

TODOs:

• Support in the load generator
• tar/untar using Rust (not tar cmd)
• Have user point to folder with code for upload, not prepared tar file
• Check / handle multiple isolation registration
• Documentation & examples in base project README
• Make code structure less brittle by searching for main.py and reqs.txt in uploaded code
• Properly build & push base containers used for this
• Test GPU containers