Function map_if_else 

pub fn map_if_else<I, O, F, S1, S2>(
    f: F,
    on_true: S1,
    on_false: S2,
) -> impl Service<I, Out = O>
where
    F: Fn(&I) -> bool,
    S1: Service<I, Out = O>,
    S2: Service<I, Out = O>,