How do I externalize my application's configurations?

I have started using Gatling today, and was wondering how can I externalize my applications variables in the form of a conf or a properties file, and then use those keys in my simulations in Gatling. I could see people passing individual properties in maven or passing properties as -Dabc=xyz but I dont want to complicate the project build files. Do you know how can I just specify properties as key value pairs?

You could use Typesafe Config, which is the library that Gatling uses too.

I tried using it. It doesnt seem to be straightforward. I am getting “null” for keys I kept in application.conf.
Pardon me, as I am new to Scala and Gatling. Do you have a simple example where a Simulation reads from test/resources/application.conf.

Here is my application.conf:

application {
    env = test

And here is how I am trying to read it in Simulation: