Circuit breaking implementation

[louyuting]

Issue Description

Circuit breaker

Describe what feature you want

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                                          |  update rules dynamically                                                                                          
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                +-------------------------+-------------------------------------------------------------------------------------------------------------------+
     entry      |                         |                                  Circuit Breaker Slot                                                             |
                |                         v                                                                                                                   |
  --------------+->                                                                                                                                           |
                |                                                                                                                                             |
                |  +-----------------------------+    +-----------------------------+    +-----------------------------+   +-----------------------------+    |
                |  | +-------------------------+ |    | +-------------------------+ |    | +-------------------------+ |   | +-------------------------+ |    |
                |  | |                         | |    | |                         | |    | |                         | |   | |                         | |    |
                |  | |  AverageRtBreakerRule   | |    | |  ErrorRatioBreakerRule  | |    | |  ErrorCountBreakerRule  | |   | |     XXXBreakerRule      | |    |
                |  | |                         | |    | |                         | |    | |                         | |   | |                         | |    |
                |  | +-----------^-------------+ |    | +------------^------------+ |    | +-----------^-------------+ |   | +------------^------------+ |    |
                |  |             |               +--->|              |              +--->|             |               +-->|              |              |    |
                |  | +-----------+-------------+ |    | +------------+------------+ |    | +-----------+-------------+ |   | +------------+------------+ |    |
                |  | | AverageRtCircuitBreaker | |    | |ErrorRatioCircuitBreaker | |    | |ErrorCountCircuitBreaker | |   | | XXXCountCircuitBreaker  | |    |
                |  | |       .CanPass()?       | |    | |       .CanPass()?       | |    | |       .CanPass()?       | |   | |       .CanPass()?       | |    |
                |  | |                         | |    | |                         | |    | |                         | |   | |                         | |    |
                |  | +-------------------------+ |    | +-------------------------+ |    | +-------------------------+ |   | +-------------------------+ |    |
                |  +-----------------------------+    +-----------------------------+    +-----------------------------+   +-----------------------------+    |
                |                                                                                                                                             |
                +---------------------------------------------------------------------------------------------------------------------------------------------+

There are Four main entity:
XXXBreakerRule: rule status machine
XXXCircuitBreaker: the check logic whether
RuleManager: manage all XXXCircuitBreakers and update rules dynamically.
CircuitBreakerSlot: As a CheckSlot to encapsulate all logic about circuit breaker.