Currently the withEnv step takes only a Groovy map of environment variables. This is cumbersome with large / complicated environments. Extra boilerplate code is required if we wish to load these from disk, which is far preferable for complex scenarios.

This feature request is for withEnv to take an argument pointing at a file in some standardized format, such as a Java .properties file, and automatically parse that into the withEnv step.

This file read should respect Groovy parsing for single-quoted and double-quoted strings for the variable values, enabling the latter to be parsed as a GString for variable expansion using the local Groovy context for substution values.