Changes made in requirement.txt for latest python version 3.8.0

[mahak933]

Before

requirement.txt contains only "flask==1.1.1."

After

Flask==2.3.3

Optional: pin core deps to compatible versions (helps reproducibility)

Jinja2==3.1.4
Werkzeug==2.3.7
itsdangerous==2.1.2
click==8.1.7

Note: Flask version change in lastest python.

Simplify the Dockerfile as well, don't need to follow such long steps.