nginx-wsgi-flask: Correct build and run failures

[OkkioXavier]

When building the docker container build failed with:

ImportError: cannot import name 'escape' from 'jinja2'

Fix:

Upgrade flask and gunicorn to remove dependency on escape

When running docker run from the flask directory the container exited immediately.

Fix:

CMD ["python", "wsgi.py"]

to

CMD ["python", "app.py"]

Functional testing:

docker-compose

docker run

[rseningen]

Upgrading requirements.txt fixes this issue

Flask==3.0.0 gunicorn==21.2.0