Deploying to production - What should be injected for ippw.IKeyStore

The below lines are mentioned at the Startup.cs
```
#if USE_TEST_KEYS
#error !!!!!!!!!!!!!!!!!!!!!! Use of test keys is only supported for testing,
DO NOT USE FOR PRODUCTION !!!!!!!!!!!!!!!!!!!!!!!!!!!!!
services.AddSingleton();
#endif
```
And we just remove those lines except ` services.AddSingleton();` to test this out. Now to deploy to production, Should we implement our own keystore class which takes the private key from a keyvault with the current setup or what is the production deployment recommendation?

从 Startup.cs 以及 issue 中提到的 ippw.IKeyStore 和 ippw.TestKeyStore 注册开始。确定并记录受支持的生产密钥存储和依赖注入配置，包括什么构成安全的生产部署；当前 issue 没有提供答案或测试。

由索引模型根据 Issue 内容生成。