Function build_signed_query_string 

pub fn build_signed_query_string<I, K, V>(
    params: I,
    credentials: &Credentials,
    recv_window: u64,
) -> Result<String>
where
    I: IntoIterator<Item = (K, V)>,
    K: AsRef<str>,
    V: AsRef<str>,

Build a signed query string with timestamp and signature.