func RequestTags(req *http.Request) []stats.Tag {
	return stats.ContextTags(req.Context())
}
RequestTags returns the tags associated with the request, if any.  It
returns nil otherwise.
package httpstats
import (
	"net/http"
	"github.com/segmentio/stats/v4"
)
func RequestWithTags(req *http.Request, tags ...stats.Tag) *http.Request {
	if stats.ContextAddTags(req.Context(), tags...) {
		return req.WithContext(req.Context())
	}
	return req.WithContext(stats.ContextWithTags(req.Context(), tags...))
}