Fix incorrect webhook time and use relative-time to display it (#24477)

Fixes #24414
After click replay this webhook, it will display `now`

![image](https://user-images.githubusercontent.com/18380374/235559399-05a23927-13f5-442d-8f10-2c7cd24022a0.png)

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

modules/timeutil/timestampnano.go

@@ -0,0 +1,28 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package timeutil
+
+import (
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// TimeStampNano is for nano time in database, do not use it unless there is a real requirement.
+type TimeStampNano int64
+
+// TimeStampNanoNow returns now nano int64
+func TimeStampNanoNow() TimeStampNano {
+	return TimeStampNano(time.Now().UnixNano())
+}
+
+// AsTime convert timestamp as time.Time in Local locale
+func (tsn TimeStampNano) AsTime() (tm time.Time) {
+	return tsn.AsTimeInLocation(setting.DefaultUILocation)
+}
+
+// AsTimeInLocation convert timestamp as time.Time in Local locale
+func (tsn TimeStampNano) AsTimeInLocation(loc *time.Location) time.Time {
+	return time.Unix(0, int64(tsn)).In(loc)
+}