[IDEA] Allow env variable substitution in CLI client properties

[tonygermano]

This came up in Mirth Slack. The user @Surbhit did not want the user/pass in clear text in the properties file or for them to be passed as arguments on the command line where they show up in the process list.

Apache commons-configuration is used throughout the project for reading .properties files, and it supports environment variable references. However, the configuration file for the CLI is read in using java.util.Properties.load, which will not perform any substitution of placeholder values.