[ISSUE #11718] Fix ErrorCode have the same code

[easynet-cn]

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What is the purpose of the change

Fix ISSUE #11718

Brief changelog

1: Define NODE_DOWN_FAILURE code 23002
2: Add test

Verifying this change

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0ee724e) 67.87% compared to head (5fc5204) 67.86%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #11747      +/-   ##
=============================================
- Coverage      67.87%   67.86%   -0.01%     
- Complexity      8895     8896       +1     
=============================================
  Files           1237     1237              
  Lines          40469    40469              
  Branches        4290     4290              
=============================================
- Hits           27469    27466       -3     
- Misses         11024    11028       +4     
+ Partials        1976     1975       -1     

Files	Coverage Δ
...java/com/alibaba/nacos/api/model/v2/ErrorCode.java	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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