Function build_layout_page_params_json 

fn build_layout_page_params_json(
    app_root: &Path,
    layout_id: Option<&str>,
    title: &str,
    body: &str,
    current_lang: Option<&str>,
    current_request_target: Option<&str>,
    has_user: bool,
    managed_business_count: i64,
) -> Option<String>

Builds layout page params JSON.