otelgin: add http.route metric attribute

[chenlujjj]

According to the Semantic conventions for HTTP metrics | OpenTelemetry, http.route is a stable label for http server metrics, I suggest to set it as a default label in the gin middleware.

[flc1125]

Can you add some unit tests?

[flc1125]

Please add a CHANGELOG: https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/CHANGELOG.md

[chenlujjj]

sure, will do

[chenlujjj]

updated unit test and changelog

[flc1125]

cc @open-telemetry/go-approvers @akats7

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.1%. Comparing base (5f609fb) to head (af3f3e7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7275     +/-   ##
=======================================
- Coverage   81.1%   81.1%   -0.1%     
=======================================
  Files        204     204             
  Lines      18148   18151      +3     
=======================================
  Hits       14728   14728             
- Misses      3001    3003      +2     
- Partials     419     420      +1     

Files with missing lines	Coverage Δ
...umentation/github.com/gin-gonic/gin/otelgin/gin.go	93.0% <100.0%> (+0.1%)	⬆️

... and 1 file with indirect coverage changes

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[chenlujjj]

Hi, @dmathieu, thanks for your comments, I've updated code and resolved them.

[dmathieu]

Note: you should avoid force-pushing your branch. It makes reviews much easier.

[chenlujjj]

@dmathieu Got it. I thought I should alway only keep one commit for the PR.

[dmathieu]

No. GitHub will squash once we merge the PR.

[chenlujjj]

That's cool. I'll keep in mind :-)