Add application_name to Connection string when using Postgres Driver

[fracca]

I am using AWS RDS Aurora with Postgres, and they can segment Database load by Application name. I have been able to set this configuration for all my other clients, but I am unable to configure this with CubeJS.

I would like to see either a new ENV variable or a configuration Option or a Default Value if nothing is set.

Looking at the "pg" package documentation, they say that this option is supported. So this change should be pretty simple and quick to implement.

Thanks Team, Keep up the great work.