optimize: fall back to any of available cluster address when query cluster address is empty

[laywin]

• I have registered the PR changes.

Ⅰ. Describe what this PR did

fall back to any of available cluster address when query cluster address is empty

Ⅱ. Does this pull request fix one issue?

fix: #6790

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

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[laywin]

@funky-eyes PTAL

[codecov]

Codecov Report

Attention: Patch coverage is 10.81081% with 33 lines in your changes missing coverage. Please review.

Project coverage is 52.16%. Comparing base (525d1b9) to head (dec1ec4).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...ache/seata/discovery/registry/RegistryService.java	0.00%	18 Missing ⚠️
.../namingserver/NamingserverRegistryServiceImpl.java	0.00%	10 Missing ⚠️
...ery/registry/consul/ConsulRegistryServiceImpl.java	0.00%	2 Missing ⚠️
...covery/registry/etcd3/EtcdRegistryServiceImpl.java	0.00%	2 Missing ⚠️
...overy/registry/nacos/NacosRegistryServiceImpl.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6797      +/-   ##
============================================
- Coverage     52.19%   52.16%   -0.03%     
- Complexity     6310     6312       +2     
============================================
  Files          1067     1067              
  Lines         37278    37303      +25     
  Branches       4427     4430       +3     
============================================
+ Hits          19456    19459       +3     
- Misses        15889    15912      +23     
+ Partials       1933     1932       -1     

Files with missing lines	Coverage Δ
...overy/registry/redis/RedisRegistryServiceImpl.java	70.90% <100.00%> (+0.17%)	⬆️
...very/registry/zk/ZookeeperRegisterServiceImpl.java	63.30% <100.00%> (+0.26%)	⬆️
...overy/registry/nacos/NacosRegistryServiceImpl.java	15.38% <0.00%> (ø)
...ery/registry/consul/ConsulRegistryServiceImpl.java	1.65% <0.00%> (-0.02%)	⬇️
...covery/registry/etcd3/EtcdRegistryServiceImpl.java	11.19% <0.00%> (-0.09%)	⬇️
.../namingserver/NamingserverRegistryServiceImpl.java	0.00% <0.00%> (ø)
...ache/seata/discovery/registry/RegistryService.java	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

[funky-eyes]

LGTM