Issue Description

Type: bug report

Describe what happened

The DefaultBlockExceptionHandler treat all BlockException as FlowException, even if it is a DegradeException. This is not good.

Describe what you expected to happen

It will set appropriate http status code and message accroding to the type of BlockException.

How to reproduce it (as minimally and precisely as possible)

1. try to create a degrade exception
2. it will get 429(too many request) and ”Blocked by Sentinel (flow limiting)"

Tell us your environment

Anything else we need to know?