polish: reduce magic value of 'NACOS_SERVER_HEADER'

[drgnchan]

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What is the purpose of the change

polish

Brief changelog

In UtilsAndCommons.java,refer NACOS_SERVER_HEADER to com.alibaba.nacos.sys.env.Constants#NACOS_SERVER_HEADER so that there is only one magic value of "Nacos-Server".

Verifying this change

1. run mvn clean:package
2. build succeed.

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[codecov-commenter]

Codecov Report

Merging #9663 (7b4730f) into develop (2d31722) will increase coverage by 0.02%.
The diff coverage is n/a.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #9663      +/-   ##
=============================================
+ Coverage      47.46%   47.48%   +0.02%     
- Complexity      4555     4556       +1     
=============================================
  Files            855      855              
  Lines          28350    28350              
  Branches        3197     3197              
=============================================
+ Hits           13456    13463       +7     
+ Misses         13668    13660       -8     
- Partials        1226     1227       +1     

Impacted Files	Coverage Δ
...com/alibaba/nacos/naming/misc/UtilsAndCommons.java	64.28% <ø> (ø)
...cos/core/cluster/remote/ClusterRpcClientProxy.java	72.85% <0.00%> (-1.43%)	⬇️
.../core/v2/event/publisher/NamingEventPublisher.java	74.68% <0.00%> (-1.27%)	⬇️
...alibaba/nacos/client/config/impl/ClientWorker.java	51.15% <0.00%> (-0.20%)	⬇️
...ent/manager/impl/ConnectionBasedClientManager.java	81.13% <0.00%> (+7.54%)	⬆️
...m/alibaba/nacos/naming/misc/HttpClientManager.java	83.33% <0.00%> (+14.28%)	⬆️

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