Upgrade project to Django 3 LTS

[garg3133]

We need to upgrade this project to atleast Django 3 LTS version as soon as possible, since Django 2 LTS has even crossed the End of extended support on April 11, 2022, which means they won't even fix any security vulnerability now in Django 2 LTS.

Please note that we cannot just upgrade to Django 3 LTS by just making a change in requirements.txt file. We need to properly go through the release notes of Django, starting with v3.0, and keep on making appropriate changes in the codebase (to make sure the update does not break anything) as we slowly update the django version.