otelgin: add routeName argument to SpanNameFormatter function

[NeoCN]

For Gin framework, the route name can only be get by using FullPath() function in gin.Context, the original SpanNameFormatter only has the http.Request argument that can not get the right route name if route parameters used.

This PR add routeName argument to SpanNameFormatter function, align with SpanNameFormatter in otelmux.

[dmathieu]

We had #4280 which didn't get traction, but did the same thing, using *gin.Context instead of a new argument.
Are there any other information from the gin context we may want to use in span name formatter?

[NeoCN]

@dmathieu Currently no other info needed from the gin.Context. Honestly, using gin.Context will be more flexible as lots of things can be got from the context. Do we need the flexibility ?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.2%. Comparing base (2dc32c1) to head (26c54e1).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5741   +/-   ##
=====================================
  Coverage   64.2%   64.2%           
=====================================
  Files        199     199           
  Lines      12454   12454           
=====================================
  Hits        8001    8001           
  Misses      4219    4219           
  Partials     234     234           

Files	Coverage Δ
...ation/github.com/gin-gonic/gin/otelgin/gintrace.go	81.1% <100.0%> (ø)
...ntation/github.com/gin-gonic/gin/otelgin/option.go	100.0% <100.0%> (ø)

[dmathieu]

Ping @hanyuancheung

[NeoCN]

@dmathieu @hanyuancheung Any suggestions for this PR?

[NeoCN]

@hanyuancheung Any suggestions? Or any principles to follow?