[SCB-2773]Change mutil dicovery registry instance merge policy (#3650)

[liubao68]

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[codecov-commenter]

Codecov Report

Merging #3651 (7ecbac8) into 2.8.x (f87a75c) will increase coverage by 0.01%.
The diff coverage is 50.00%.

❗ Current head 7ecbac8 differs from pull request most recent head d2073ce. Consider uploading reports for the commit d2073ce to get more accurate results

@@             Coverage Diff              @@
##              2.8.x    #3651      +/-   ##
============================================
+ Coverage     74.38%   74.39%   +0.01%     
  Complexity      679      679              
============================================
  Files          1590     1590              
  Lines         39952    39953       +1     
  Branches       3655     3655              
============================================
+ Hits          29719    29724       +5     
+ Misses         8740     8738       -2     
+ Partials       1493     1491       -2     

Impacted Files	Coverage Δ
...org/apache/servicecomb/registry/api/Discovery.java	0.00% <ø> (ø)
...stry/lightweight/AbstractLightweightDiscovery.java	0.00% <0.00%> (ø)
.../servicecomb/localregistry/LocalRegistryStore.java	92.45% <ø> (ø)
...e/servicecomb/schemadiscovery/SchemaDiscovery.java	53.65% <ø> (ø)
...cecomb/serviceregistry/ServiceCenterDiscovery.java	93.33% <ø> (ø)
...b/registry/api/registry/MicroserviceInstances.java	97.14% <66.66%> (-0.16%)	⬇️
.../apache/servicecomb/registry/DiscoveryManager.java	96.61% <100.00%> (+0.05%)	⬆️
...ache/servicecomb/localregistry/LocalDiscovery.java	85.71% <100.00%> (ø)
...mb/config/ConfigCenterConfigurationSourceImpl.java	10.63% <0.00%> (+1.06%)	⬆️
...he/servicecomb/foundation/common/net/NetUtils.java	66.40% <0.00%> (+1.60%)	⬆️
... and 2 more

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