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

tools/goctl/api/gogen/handler.tpl

@@ -0,0 +1,26 @@
+package {{.PkgName}}
+
+import (
+	"net/http"
+
+	{{if .After1_1_10}}"github.com/zeromicro/go-zero/rest/httpx"{{end}}
+	{{.ImportPackages}}
+)
+
+func {{.HandlerName}}(svcCtx *svc.ServiceContext) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		{{if .HasRequest}}var req types.{{.RequestType}}
+		if err := httpx.Parse(r, &req); err != nil {
+			httpx.Error(w, err)
+			return
+		}
+
+		{{end}}l := {{.LogicName}}.New{{.LogicType}}(r.Context(), svcCtx)
+		{{if .HasResp}}resp, {{end}}err := l.{{.Call}}({{if .HasRequest}}&req{{end}})
+		if err != nil {
+			httpx.Error(w, err)
+		} else {
+			{{if .HasResp}}httpx.OkJson(w, resp){{else}}httpx.Ok(w){{end}}
+		}
+	}
+}