feature: init namingserver client

[ggbocoder]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Seata client for invoking the Naming Server

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 7.32394% with 329 lines in your changes missing coverage. Please review.

Project coverage is 50.53%. Comparing base (fff45ce) to head (18d3db4).
Report is 94 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
.../namingserver/NamingserverRegistryServiceImpl.java	0.00%	237 Missing ⚠️
...in/java/org/apache/seata/common/metadata/Node.java	14.28%	26 Missing and 4 partials ⚠️
.../src/main/java/org/apache/seata/server/Server.java	10.00%	17 Missing and 1 partial ⚠️
...a/org/apache/seata/common/util/HttpClientUtil.java	38.09%	13 Missing ⚠️
...e/seata/common/metadata/namingserver/Instance.java	50.00%	7 Missing ⚠️
...common/metadata/namingserver/NamingServerNode.java	33.33%	6 Missing ⚠️
...registry/namingserver/NamingRegistryException.java	0.00%	6 Missing ⚠️
...pache/seata/common/metadata/namingserver/Unit.java	0.00%	4 Missing ⚠️
.../apache/seata/discovery/registry/RegistryType.java	0.00%	2 Missing ⚠️
...try/namingserver/NamingserverRegistryProvider.java	0.00%	2 Missing ⚠️
... and 2 more

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6536      +/-   ##
============================================
- Coverage     50.99%   50.53%   -0.46%     
- Complexity     5923     5926       +3     
============================================
  Files          1058     1061       +3     
  Lines         36779    37082     +303     
  Branches       4369     4399      +30     
============================================
- Hits          18754    18738      -16     
- Misses        16131    16445     +314     
- Partials       1894     1899       +5     

Files with missing lines	Coverage Δ
...mon/src/main/java/org/apache/seata/common/XID.java	92.30% <ø> (ø)
...he/seata/namingserver/entity/pojo/ClusterData.java	63.79% <100.00%> (ø)
.../apache/seata/discovery/registry/RegistryType.java	0.00% <0.00%> (ø)
...try/namingserver/NamingserverRegistryProvider.java	0.00% <0.00%> (ø)
...eata/namingserver/controller/NamingController.java	37.83% <0.00%> (-1.06%)	⬇️
...ache/seata/namingserver/manager/NamingManager.java	59.13% <0.00%> (ø)
...pache/seata/common/metadata/namingserver/Unit.java	0.00% <0.00%> (ø)
...common/metadata/namingserver/NamingServerNode.java	37.03% <33.33%> (+17.80%)	⬆️
...registry/namingserver/NamingRegistryException.java	0.00% <0.00%> (ø)
...e/seata/common/metadata/namingserver/Instance.java	41.79% <50.00%> (-1.07%)	⬇️
... and 4 more

... and 9 files with indirect coverage changes

[funky-eyes]

LGTM