Function register_string_configuration 

pub fn register_string_configuration<T: ConfigurationValue<ValkeyString>>(
    ctx: &Context,
    name: &str,
    variable: &'static T,
    default: &str,
    flags: ConfigurationFlags,
    on_changed: Option<Box<dyn Fn(&ConfigurationContext, &str, &'static T)>>,
    on_set: Option<Box<dyn Fn(&ConfigurationContext, &str, &'static T) -> Result<(), ValkeyError>>>,
)