Disable Sign Up config option for Internal Apps/Services?

I was wondering if/when this project will include the disable sign up config from [v4.8.0](https://github.com/firebase/firebaseui-web/releases/tag/v4.8.0) of firebaseui-web for [configuring the email provider](https://github.com/firebase/firebaseui-web#configure-email-provider)?

I feel like this would be a necessary option to have for this project as it is needed for internal web services and would love to be able to tap into this feature while keeping it all in react.

首先，将 firebaseui-web v4.8.0 版本及其“configure email provider”文档与 React 包装器的配置接口进行比较。当可以为内部服务配置禁用注册选项，同时保留 React 集成且行为与 firebaseui-web 一致时，工作即告完成。

由索引模型根据 Issue 内容生成。