Migrate from CircleCI to GitHub actions

[chocoelho]

Description

This PR migrates our building system from CircleCI to Github Actions. It also pins pylint-django and Django dependencies, as they're required to be this way in order to properly build. nightly and main workflows have a shared build action, which aims to avoid duplication of context and code, which may lead to maintainability issues in the future if it wasn't implemented this way.

Motivation and Context

See https://github.com/vintasoftware/django-react-boilerplate/issues/554. This PR resolves https://github.com/vintasoftware/django-react-boilerplate/issues/554 too.

Screenshots (if appropriate):

Non applicable

Steps to reproduce (if appropriate):

• Check Actions tab in the current repo.
• Create a test project following the steps described on README.md

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires documentation updates.
• [x] I have updated the documentation accordingly.
• [x] My change requires dependencies updates.
• [x] I have updated the dependencies accordingly.