feat(middleware): add sunset/deprecation header middleware

[thedevsaddam]

This PR will include a Sunset middleware which can be used to deprecate an endpoint or a group of endpoints.

For additional information please go through the LINK

Example usages

func main() {
	r := chi.NewRouter()

	sunsetAt := time.Date(2025, 12, 24, 10, 20, 0, 0, time.UTC)
	r.Use(middleware.Sunset(sunsetAt))

	// can provide additional link for updated resource
	// r.Use(middleware.Sunset(sunsetAt, "https://example.com/v1/deprecation-details"))

	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("This endpoint will be removed soon"))
	})

	log.Println("Listening on port: 3000")
	http.ListenAndServe(":3000", r)
}

[VojtechVitek]

I like this feature. However, should we wait for the Sunset header to actually make it into an RFC?

[VojtechVitek]

LGTM.

I think this is useful, especially since these headers are defined in RFC8594 - https://www.rfc-editor.org/rfc/rfc8594.html.

Let's see if @pkieltyka agrees this can be merged into github.com/go-chi/chi/v5/middleware :)

[pkieltyka]

thanks for the PR @thedevsaddam and thanks for reviewing @VojtechVitek

[thedevsaddam]

thanks for the PR @thedevsaddam and thanks for reviewing @VojtechVitek

Thank you so much for this amazing package!