Function encode_set_user 

pub fn encode_set_user(
    operation_type: DataOperationTypeEnum,
    user_index: u16,
    user_name: Nullable<String>,
    user_unique_id: Nullable<u32>,
    user_status: Nullable<UserStatusEnum>,
    user_type: Nullable<UserTypeEnum>,
    credential_rule: Nullable<CredentialRuleEnum>,
) -> Vec<u8> 

Encode the SetUser command request payload.