[Dubbo-3653] Enable etcd to support metadata center

[ralf0131]

What is the purpose of the change

#3653 Support etcd as metadata center

Brief changelog

• Support etcd as metadata center
• Add unit test

Verifying this change

• Local test passed

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[codecov-io]

Codecov Report

Merging #3943 into master will increase coverage by 0.5%.
The diff coverage is 74.19%.

@@             Coverage Diff             @@
##             master    #3943     +/-   ##
===========================================
+ Coverage     63.71%   64.22%   +0.5%     
- Complexity       71       98     +27     
===========================================
  Files           713      715      +2     
  Lines         31471    31494     +23     
  Branches       5075     5077      +2     
===========================================
+ Hits          20053    20226    +173     
+ Misses         9125     8940    -185     
- Partials       2293     2328     +35

Impacted Files	Coverage Δ	Complexity Δ
...bo/metadata/store/consul/ConsulMetadataReport.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...dubbo/metadata/support/AbstractMetadataReport.java	71.09% <100%> (-0.66%)	0 <0> (ø)
...adata/store/zookeeper/ZookeeperMetadataReport.java	75% <100%> (+0.92%)	0 <0> (ø)	⬇️
...metadata/store/etcd/EtcdMetadataReportFactory.java	100% <100%> (ø)	0 <0> (?)
...ubbo/metadata/store/redis/RedisMetadataReport.java	100% <100%> (ø)	0 <0> (ø)	⬇️
.../dubbo/metadata/identifier/MetadataIdentifier.java	60.46% <100%> (ø)	0 <0> (ø)	⬇️
.../dubbo/metadata/store/etcd/EtcdMetadataReport.java	68.18% <68.18%> (ø)	0 <0> (?)
...apache/dubbo/common/config/ConfigurationUtils.java	64% <0%> (-8%)	0% <0%> (ø)
...ava/org/apache/dubbo/config/DubboShutdownHook.java	75% <0%> (-6.25%)	0% <0%> (ø)
...ng/exchange/support/header/HeartbeatTimerTask.java	73.68% <0%> (-5.27%)	0% <0%> (ø)
... and 18 more

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