Set up enforced forwarding to https if not running locally

[AetherUnbound]

It would appear that Heroku doesn't automatically forward HTTP requests to HTTPS, and since we aren't handling the load balancing on the Heroku end we'll need to do this from Django.

There are a few guides for doing exactly this:

• https://elitwilliams.medium.com/how-to-redirect-all-traffic-to-https-from-http-for-django-3-apps-hosted-on-heroku-63f8fbbfab2a
• https://stackoverflow.com/a/49112565/3277713

We'll want to set this up to be disabled locally since that's fine to be over HTTP (and would be difficult to set up HTTPS locally).

[AetherUnbound]

The fix in #51 broke deployments, unfortunately. We'll have to look into how this change affects the baking we do for Netlify.

[AetherUnbound]

Note: This also broke the Netlify build deployment callbacks since it was using http. If we are able to address this, we'll need to update that link too (and verify it works).