fix: revise kafka sink conf/metrics

[Yisaer]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 22 lines in your changes missing coverage. Please review.

Project coverage is 71.10%. Comparing base (0c6f4a0) to head (b4b2cac).
Report is 15 commits behind head on master.

Files with missing lines	Patch %	Lines
extensions/impl/kafka/sink.go	58.06%	11 Missing and 2 partials ⚠️
metrics/metrics.go	0.00%	5 Missing ⚠️
extensions/impl/sql/sink.go	50.00%	3 Missing ⚠️
extensions/impl/kafka/source.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3494      +/-   ##
==========================================
+ Coverage   71.07%   71.10%   +0.04%     
==========================================
  Files         416      417       +1     
  Lines       48001    48042      +41     
==========================================
+ Hits        34112    34159      +47     
+ Misses      11219    11215       -4     
+ Partials     2670     2668       -2     

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