[feature] Circuit breaker for "hot-spot" values | 热点参数熔断降级支持

目前Sentinel支持了热点参数限流，而在某些场景，下游可能对不同参数有不同处理方式，那么上游可能就需要根据参数的处理情况做降级规则的配置，从而保护自身系统的稳定性。
想问一下是否有必要支持这种场景，还是说建议使用者使用参数作为资源名的方式来实现这个需求。
目前想法是结合热点参数限流和降级两种规则，实现一套新的热点参数降级规则

Start by clarifying whether parameter-based resource names are sufficient or whether a separate hot-spot degradation rule is needed. Define how hot-spot parameter rate limiting should combine with degradation rules and what behavior would count as complete before locating the relevant implementation and tests.

Written by the indexing model from the issue text.