feat: use go:embed to embed templates (#1756)

tools/goctl/api/gogen/genmiddleware.go

@@ -1,6 +1,7 @@
 package gogen
 
 import (
+	_ "embed"
 	"strings"
 
 	"github.com/zeromicro/go-zero/tools/goctl/api/spec"
@@ -8,27 +9,8 @@ import (
 	"github.com/zeromicro/go-zero/tools/goctl/util/format"
 )
 
-var middlewareImplementCode = `
-package middleware
-
-import "net/http"
-
-type {{.name}} struct {
-}
-
-func New{{.name}}() *{{.name}} {	
-	return &{{.name}}{}
-}
-
-func (m *{{.name}})Handle(next http.HandlerFunc) http.HandlerFunc {
-	return func(w http.ResponseWriter, r *http.Request) {
-		// TODO generate middleware implement function, delete after code implementation
-
-		// Passthrough to next handler if need 
-		next(w, r)
-	}	
-}
-`
+//go:embed middleware.tpl
+var middlewareImplementCode string
 
 func genMiddleware(dir string, cfg *config.Config, api *spec.ApiSpec) error {
 	middlewares := getMiddleware(api)