feat(examples): Introduce HTTP Flask server as example

[razvand]

Introduce an HTTP Flask server as binary compatibility run. Install Python + Flask using Dockerfile. Use the unikraft.org/python:3.12 registry image.

Add typical files for a bincompat app:

• Kraftfile: build / run rules, including pulling the unikraft.org/python:3.12 image
• Dockerfile: filesystem, including binary and libraries
• README.md: instructions to set up, build and run the application
• requirements.txt: Python / Pip requirements file
• server.py: simple Flask HTTP server implementation

[razvand]

I get this error when running, any ideas?

/tmp/kraft-run-1758828628/unikraft/bin/kernel: can't open file '/usr/bin/python3': [Errno 2] No such file or directory

@StefanJum , we need to upstream Python.