docs: improve contribution documentation (#5540)

http/headers_dev.go

@@ -1,14 +0,0 @@
-//go:build dev
-
-package http
-
-// global headers to append to every response
-// cross-origin headers are necessary to be able to
-// access them from a different URL during development
-var globalHeaders = map[string]string{
-	"Cache-Control":                    "no-cache, no-store, must-revalidate",
-	"Access-Control-Allow-Origin":      "*",
-	"Access-Control-Allow-Headers":     "*",
-	"Access-Control-Allow-Methods":     "*",
-	"Access-Control-Allow-Credentials": "true",
-}