Function validate_with_env 

pub fn validate_with_env(
    options: &mut WrapperOptions,
    env: &dyn Fn(&str) -> Option<String>,
) -> Result<(), String>

Resolve options.init to Some(bool): the flag if one was given (None means none), otherwise the environment default for docker launches. Idempotent, because validation may run again on options it already resolved: --no-init (or a resolved false) without docker is the default anyway and is accepted.