Fix url generated from ConfigCenterConfig missed 'config.' prefix

[chickenlj]

What is the purpose of the change

see #3872

Brief changelog

XXXXX

Verifying this change

XXXXX

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[zhaixiaoxiang]

I also encounter this BUG. I've verified this modification. LGTM

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (2.7.3-release@cfba520). Click here to learn what that means.
The diff coverage is 100%.

@@               Coverage Diff                @@
##             2.7.3-release    #4411   +/-   ##
================================================
  Coverage                 ?   63.53%           
  Complexity               ?      452           
================================================
  Files                    ?      766           
  Lines                    ?    33639           
  Branches                 ?     5385           
================================================
  Hits                     ?    21374           
  Misses                   ?     9842           
  Partials                 ?     2423

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/rpc/protocol/AsyncToSyncInvoker.java	87.5% <ø> (ø)	0 <0> (?)
...va/org/apache/dubbo/config/ConfigCenterConfig.java	83.07% <100%> (ø)	0 <0> (?)

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