Add support for using OS environement variables

[ghost]

This is more related to private registries and applications, but can be useful on mudles too. Sometimes configuration like paths to XSD files and certs are set at the OS level in the environment variables, and at times this might even be pulled through to the OS from secrets on your cloud solution. It will be helpful is these environment variables are accessible by the module.xml.

[daimor]

IPM already supports expressions, and you can use it this way, for instance in this case we read environment variable ISC_PACKAGE_INSTALLDIR, " needs instead of " "#{$system.Util.GetEnviron("ISC_PACKAGE_INSTALLDIR")}"

[ghost]

Thank you. I did not see this on an example or documentation. And working through all the code takes too much time.