support set http metric namespace

[UnderTreeTech]

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[codecov-commenter]

Codecov Report

Merging #113 (735352b) into master (e458d8e) will increase coverage by 0.42%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master     #113      +/-   ##
==========================================
+ Coverage   80.13%   80.55%   +0.42%     
==========================================
  Files          36       36              
  Lines        1948     1949       +1     
==========================================
+ Hits         1561     1570       +9     
+ Misses        292      285       -7     
+ Partials       95       94       -1     

Impacted Files	Coverage Δ
pkg/server/http/middlewares/metric.go	81.81% <71.42%> (+81.81%)	⬆️
pkg/server/http/server/server.go	70.00% <100.00%> (+4.37%)	⬆️

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