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/user.go

@@ -0,0 +1,31 @@
+// Copyright 2014 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 (
+	"fmt"
+)
+
+// User represents a API user.
+type User struct {
+	ID        int64  `json:"id"`
+	UserName  string `json:"username"` // LEGACY [Gogs 1.0]: remove field(s) for backward compatibility
+	Login     string `json:"login"`
+	FullName  string `json:"full_name"`
+	Email     string `json:"email"`
+	AvatarUrl string `json:"avatar_url"`
+}
+
+func (c *Client) GetUserInfo(user string) (*User, error) {
+	u := new(User)
+	err := c.getParsedResponse("GET", fmt.Sprintf("/users/%s", user), nil, nil, u)
+	return u, err
+}
+
+func (c *Client) GetSelfInfo() (*User, error) {
+	u := new(User)
+	err := c.getParsedResponse("GET", "/user", nil, nil, u)
+	return u, err
+}