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/admin_org.go

@@ -0,0 +1,43 @@
+// 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 (
+	"bytes"
+	"encoding/json"
+	"fmt"
+)
+
+func (c *Client) AdminCreateOrg(user string, opt CreateOrgOption) (*Organization, error) {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return nil, err
+	}
+	org := new(Organization)
+	return org, c.getParsedResponse("POST", fmt.Sprintf("/admin/users/%s/orgs", user),
+		jsonHeader, bytes.NewReader(body), org)
+}
+
+func (c *Client) AdminCreateTeam(user string, opt CreateTeamOption) (*Team, error) {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return nil, err
+	}
+	team := new(Team)
+	return team, c.getParsedResponse("POST", fmt.Sprintf("/admin/orgs/%s/teams", user),
+		jsonHeader, bytes.NewReader(body), team)
+}
+
+func (c *Client) AdminAddTeamMembership(teamID int64, user string) error {
+	_, err := c.getResponse("PUT", fmt.Sprintf("/admin/teams/%d/members/%s", teamID, user),
+		jsonHeader, nil)
+	return err
+}
+
+func (c *Client) AdminAddTeamRepository(teamID int64, repo string) error {
+	_, err := c.getResponse("PUT", fmt.Sprintf("/admin/teams/%d/repos/%s", teamID, repo),
+		jsonHeader, nil)
+	return err
+}