Values from the default value provider should be interpolated

[remkop]

(From discussion on #1566)
Currently, if the values retrieved from the default value provider contain a variable, these variables are not interpolated.

Interpolating these variables allows default values to be retrieved from:

1. system properties
2. environment variables
3. resource bundles
4. and finally, the fallback value

It also allows CLI applications to have configuration files for default values where the end users can specify the key used to look up values in the system properties or environment variables, and use different keys for each.