Add background task to check for new config content

[datadavev]

NAAN config updates are currently checked by a cron task.

A couple alternatives:

1. An alternative option may be to use a background task in the resolver service.
2. Add a new service in python that performs background tasks including grabbing config changes.

Option 2 might offer more flexibility, though ultimately the same as being run under cron.

Option 1 would limit future deployments to live servers only since background tasks are generally not supported in serverless infrastructure.