Add support to migrate from gogs (#14342)

Add support to migrate gogs:

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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Andrew Thornton <art27@cantab.net>

vendor/github.com/gogs/go-gogs-client/utils.go

@@ -0,0 +1,23 @@
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gogs
+
+import (
+	"net/http"
+)
+
+var jsonHeader = http.Header{"content-type": []string{"application/json"}}
+
+func Bool(v bool) *bool {
+	return &v
+}
+
+func String(v string) *string {
+	return &v
+}
+
+func Int64(v int64) *int64 {
+	return &v
+}