[Consumer] [Discovery] Treat consumer message processing like a Django request

[robrap]

Is there a more general solution possible in Django for calling Django's typical before-request and after-request code when processing each message? This might provide an alternate solution to edx/edx-arch-experiments#158.

Maybe this isn't a high-priority, but I wonder what issues may be lurking that we just wouldn't be aware of.

[robrap]

This is replacing the ticket [Consumer] Better replication of Django requests in consumer infinite loop which was created in a different repo, and had no description.