provide FromJSON ConnectInfo instance for easy configuration

[peterbecich]

I think it would be helpful to provide instance FromJSON ConnectInfo for reading ConnectInfo from JSON or YAML.

i.e. via loadYamlSettings: https://hackage.haskell.org/package/yaml-0.11.11.2/docs/Data-Yaml-Config.html#v:loadYamlSettings

[peterbecich]

@phadej please review

[phadej]

My quick review is:

• I think this is a bad idea. Especially by using generics, but even if it were manually written instance, you are tying somewhat internal type of the library to possibly public interface. That creates maintenance problems.
• There is true and better way: make people supply connection strings or urls. These are well documented https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING