Add an abstract json layout to make it's easier to change json library (#16528)

* Add an abstract json layout to make it's easier to change json library

* Fix import

* Fix import sequence

* Fix blank lines

* Fix blank lines

modules/private/mail.go

@@ -10,8 +10,8 @@ import (
 	"io/ioutil"
 	"net/http"
 
+	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/setting"
-	jsoniter "github.com/json-iterator/go"
 )
 
 // Email structure holds a data for sending general emails
@@ -33,7 +33,6 @@ func SendEmail(ctx context.Context, subject, message string, to []string) (int,
 
 	req := newInternalRequest(ctx, reqURL, "POST")
 	req = req.Header("Content-Type", "application/json")
-	json := jsoniter.ConfigCompatibleWithStandardLibrary
 	jsonBytes, _ := json.Marshal(Email{
 		Subject: subject,
 		Message: message,