Feature: lint python

[LoTerence]

Fixes #407

This PR installs and configures Black, isort, and flake8 linters and formatter for the python backend.

• I used this link to help: https://programmingmylife.com/2023-01-21-code-formatting-configs-in-django.html

To test, run these commands in the /backend folder:

1. poetry install
2. poetry run black .
3. poetry run isort .
4. poetry run flake8

Changes

• Installed Black formatter
• Ran poetry run black . to reformat the entire python backend.
• This^ command mostly just changed single quote strings to double quotes in 9 different files
• Installed flake8 linter
• Configured flake8 settings to not conflict with Black
• Installed isort
• configured isort settings to sync with Black and flake8
• Ran poetry run isort . to sort the imports

My next optional suggestion: adding pre-commit hooks that automates linting and formatting before every commit:

• https://builtwithdjango.com/blog/improve-your-code-with-pre-commit
• We can also automate pre-commit hooks with Github Actions