unify config-center model

[chickenlj]

What is the purpose of the change

related issues: #4247

docs: apache/dubbo-website#388

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[codecov-io]

Codecov Report

Merging #4388 into 2.7.3-release will increase coverage by 0.03%.
The diff coverage is 45%.

@@                 Coverage Diff                 @@
##             2.7.3-release    #4388      +/-   ##
===================================================
+ Coverage             63.5%   63.54%   +0.03%     
  Complexity             452      452              
===================================================
  Files                  765      765              
  Lines                32690    32680      -10     
  Branches              5149     5150       +1     
===================================================
+ Hits                 20761    20766       +5     
+ Misses                9542     9523      -19     
- Partials              2387     2391       +4

Impacted Files	Coverage Δ	Complexity Δ
...figcenter/support/nop/NopDynamicConfiguration.java	71.42% <ø> (ø)	0 <0> (ø)	⬇️
...apache/dubbo/common/constants/CommonConstants.java	100% <ø> (ø)	0 <0> (ø)	⬇️
...ter/support/apollo/ApolloDynamicConfiguration.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...org/apache/dubbo/registry/nacos/NacosRegistry.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...onfigcenter/consul/ConsulDynamicConfiguration.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...enter/support/nacos/NacosDynamicConfiguration.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...gcenter/support/etcd/EtcdDynamicConfiguration.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...g/apache/dubbo/config/AbstractInterfaceConfig.java	72% <0%> (ø)	0 <0> (ø)	⬇️
...e/dubbo/registry/integration/RegistryProtocol.java	82.69% <100%> (ø)	0 <0> (ø)	⬇️
.../dubbo/registry/integration/RegistryDirectory.java	80.3% <100%> (ø)	0 <0> (ø)	⬇️
... and 14 more

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[ralf0131]

LGTM.