[ENHANCEMENT] robot.toml: Support for env variables in list values

[simonmeggle]

It would be great if robot.toml would support to use an environment variable in a list value:

[profiles.bcs.pre-run-modifiers]
"robots/Lib/TestGenerator.py" = [{ expr = "client_index=" + environ.get('AWS_BATCH_JOB_ARRAY_INDEX')" }]

Thanks 👍