Function admin_router 

pub fn admin_router(
    state: AdminState,
    metrics_handle: MetricsHandle,
    session_handle: SessionHandle,
    cache_handle: Option<CacheHandle>,
    proxy: McpProxy,
    config: &ProxyConfig,
    config_path: Option<PathBuf>,
    cb_handles: HashMap<String, CircuitBreakerHandle>,
) -> Router

Build the admin API router.