Move configuration of Lassie from startup to a per fetch basis.

We can currently have configuration for a Lassie instance that is used on startup, but we have slowly added features that allow that same configuration on a per fetch basis. Documentation around this might be confusing or not very straightforward for a user trying to use Lassie. We have started to favor per fetch configuration. We should move the configuration from the initialization of a Lassie instance to the fetch call.