Update Dockerfile to use Python virtual environment

[LeBaronDeCharlus]

Fix the build error

STEP 5/9: RUN pip3 install --no-cache-dir boxes flask lolcat requests -r requirements.txt
error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try apt install
    python3-xyz, where xyz is the package you are trying to
    install.

    If you wish to install a non-Kali-packaged Python package,
    create a virtual environment using python3 -m venv path/to/venv.
    Then use path/to/venv/bin/python and path/to/venv/bin/pip. Make
    sure you have pypy3-venv installed.

    If you wish to install a non-Kali-packaged Python application,
    it may be easiest to use pipx install xyz, which will manage a
    virtual environment for you. Make sure you have pipx installed.

    For more information, refer to the following:
    * https://www.kali.org/docs/general-use/python3-external-packages/
    * /usr/share/doc/python3.13/README.venv

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.
Error: building at STEP "RUN pip3 install --no-cache-dir boxes flask lolcat requests -r requirements.txt": while running runtime: exit status 1