Update package tooling and boilerplate

[willbarton]

This change updates our tooling to make a few changes and updates:

• Use Ruff exclusively for formatting, linting, and import-sorting. Ruff can replace Black and isort, and is faster.
• Add Bandit for static security analysis.
• Move to pyproject.toml
• Add setuptools_scm for versioning. This will mean we don't have to manually update a version number in pyproject.toml.
• Run ruff check --fix for linting fixes
• Updates our officially supported versions of Django, Wagtail, and Django-Flags to the most recent versions