polly 可用于异常的熔断降级，重试等
官方： https://github.com/App-vNext/Polly
Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner
Polly是一个.NET弹性和瞬时故障处理库，它允许开发人员以流畅且线程安全的方式表达策略，如重试、断路器、超时、隔板隔离和回退
