Function attach 

pub fn attach(
    db_name: &str,
    user: &str,
    pass: &str,
    protocol: ProtocolVersion,
    charset: Charset,
    role_name: Option<&str>,
    dialect: Dialect,
    no_db_triggers: bool,
    auth_plugin: Option<&AuthPlugin>,
    srp_key: &[u8; 32],
) -> Result<Bytes, FbError>

Attach request