Function build_config 

pub fn build_config(
    store_id: &str,
    device_id: &str,
    store_name: &str,
    join_info: &CloudHomeJoinInfo,
    cipher: &CloudCipher,
) -> Config

Build the Config struct from join/restore parameters. The cipher records the home’s storage mode: Encrypted ⇒ opaque (a store key is stored, with its fingerprint), Plaintext ⇒ browsable (no key, no fingerprint).