Minor refactor to decouple config from the rest of the app

[drdrsh]

Today, if we want to import config crate, we have to import the entire universe because reload_config references ConnectionPool and importing ConnectionPool cascades into importing the entire app.

This refactor removes reload_config from config.rs and places it in main.rs

This will allow us to import the config crate into external binaries that want to serialize/deserialize configs without having to import the entire app.