otelgin: Add a WithSpanStartOptions option

[arshukla98]

Closes: #7247

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.2%. Comparing base (abb5c4f) to head (50403a2).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7261     +/-   ##
=======================================
- Coverage   81.2%   81.2%   -0.1%     
=======================================
  Files        207     207             
  Lines      18263   18270      +7     
=======================================
+ Hits       14835   14839      +4     
- Misses      3007    3009      +2     
- Partials     421     422      +1     

Files with missing lines	Coverage Δ
...ntation/github.com/gin-gonic/gin/otelgin/config.go	100.0% <100.0%> (ø)
...umentation/github.com/gin-gonic/gin/otelgin/gin.go	93.1% <100.0%> (+0.1%)	⬆️

... and 1 file with indirect coverage changes

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[dmathieu]

This is missing tests and a changelog entry.

[flc1125]

What is the reason for moving this part here?

[arshukla98]

This structure is also used in otelhttp, as seen [here](

opentelemetry-go-contrib/instrumentation/net/http/otelhttp/handler.go

Lines 52 to 60 in f368d04

	func NewMiddleware(operation string, opts ...Option) func(http.Handler) http.Handler {
	h := middleware{
	operation: operation,
	}
	defaultOpts := []Option{
	WithSpanOptions(trace.WithSpanKind(trace.SpanKindServer)),
	WithSpanNameFormatter(defaultHandlerFormatter),
	}

).

Let me know if you’d prefer to remove it.

[flc1125]

According to the principle of Occam's Razor: Do not multiply entities beyond necessity.

From what I understand, the operating result would be the same even without modifying this part.

[flc1125]

Additionally, please correct the title of this PR.

[flc1125]

If you are ready for review, you can remove the draft mode.