This models the runtime environment of the shell where the app is running. Optionally pass a separator to use for multi-values otherwise a standard comma is used - this means you MUST override the separator if you have single values which contain commas, otherwise singular environment keys will just retrieve the first value.
This models the key used to get a value out of the Environment using the standard Lens mechanic. Note that if your values contain commas, either use a EnvironmentKey.(mapping).multi.required()/optional()/defaulted() to retrieve the entire list, or override the comma separator in your initial Environment.