Environment variable in configuration file does not work

[YanchunHe]

Describe the bug

Variables in ref.toml such as:

[paths]
log = "${REF_CONFIGURATION}/log"
scratch = "${REF_CONFIGURATION}/scratch"
software = "${REF_CONFIGURATION}/software"
results = "${REF_CONFIGURATION}/results"
dimensions_cv = "${REF_INSTALLATION_DIR}/packages/climate-ref-core/src/climate_ref_core/pycmec/cv_cmip7_aft.yaml"

does not work if these variables are set in the .bashrc/.zshrc, by export REF_CONFIGURATION=xxxx

Maybe this is used only for demonstration as placeholder for the path, but seems to be somehow confusing.

btw, this has been raised in the REF feedback online session on 11st June.