Add SSO login using `django-allauth` to django client

### Overview

The django app needs to have SSO login functionality. It's easier that it be to a common single sign-on service like Google, for which there are plenty of guides available on the web.

### Action Items

- [ ] Add Single Sign-On functionality using Google
- [ ] Make sure sign in and sign out works
- [ ] Add documentation for another developer to set this up.

### Resources/Instructions

We don't really need this step, and really we will throw away the Google authentication later. But there's so many guides about this that it's an easier path to make this the first step in setting up SSO.

- django-allauth docs
- search the web for guides on "django google authentication"
- the "login page" and "add google login" commits in the [django-party repo](https://github.com/fyliu/django-party/commits/main/?before=9f17eb937cb5020341cce75cd18eab946bfb9f86+35) might be helpful also.

Notes:

1. There's some manual steps to set things up on the Google side and also steps to set it up in the Django admin site. Just follow those at first to get it working.

1. Then, I think there's a way to specify the Django configurations in a config file or a `.env` file. If there is, it would be preferable. It would save some steps in the setup for whoever tries to use this.

1. The sign in/out may need some django frontend changes. Since we just want the functionality. It's fine to do the simplest things in the backend to get it working.

1. There's also a more modern way to make it act like a single page application, using htmx/alpine.js . That's okay too if it doesn't take a lot of effort.