Problem

Stems from #2566. See that issue for background.

Blocked by #2789

Description

Convert the Django app to an ASGI application.

Replace the gunicorn worker from #2788 with an appropriate ASGI-capable worker. Subclass the worker to add ASGI lifecycle support and update the session-sharing implementation from #2788 to use the application lifecycle rather than worker lifecycle. Application lifecycle is more flexible and allows us to switch deployment contexts more easily.