refactor: gin prometheus for api

[rfyiamcool]

summary

1. if don't close http.response.body, throw resource leak. ( goroutine leak and fd leak)
2. replace io.ReadAll to io.ioutil, io.ioutil is deprecated in go1.16.
3. use gin.context.FullPATH, because gin.Request.URL.PATH is full url with query params. e.g. prometheus only need to record /article/:uid url, don't need /article/13183?page_index=10&page=100&q=xxx&order=desc. when the url is randomized, this design is not friendly to prome storage and does not display well in grafana.
4. refactor the code.

[sweep-ai]

Apply Sweep Rules to your PR?

• Apply: All new business logic should have corresponding unit tests.
• Apply: Refactor large functions to be more modular.

[codecov]

Codecov Report

Merging #1371 (3c9fd05) into main (2496a16) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #1371   +/-   ##
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  Coverage   4.30%   4.30%           
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  Files         45      45           
  Lines       3809    3809           
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  Hits         164     164           
  Misses      3634    3634           
  Partials      11      11