In this commit, we expand the dev build's DevConfig options struct with
Postgres and SQL backend options that can be used to initialise the
account store.
In this commit, we introduce a DevConfig struct which is embedded in the
main lit Config struct. It is defined in two separate files that are
made mutually exclusive using the `dev` build tag. The idea of this
struct is that it allows us to expose additional config options to LiT
if we build in a development environment such as our itests. In other
words, we will be able to start developing features and testing them
before making them available to users via the production build.
As of this commit, both implementations of the struct are the same.
