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/org.go

@@ -0,0 +1,69 @@
+// 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"
+)
+
+type Organization struct {
+	ID          int64  `json:"id"`
+	UserName    string `json:"username"`
+	FullName    string `json:"full_name"`
+	AvatarUrl   string `json:"avatar_url"`
+	Description string `json:"description"`
+	Website     string `json:"website"`
+	Location    string `json:"location"`
+}
+
+func (c *Client) ListMyOrgs() ([]*Organization, error) {
+	orgs := make([]*Organization, 0, 5)
+	return orgs, c.getParsedResponse("GET", "/user/orgs", nil, nil, &orgs)
+}
+
+func (c *Client) ListUserOrgs(user string) ([]*Organization, error) {
+	orgs := make([]*Organization, 0, 5)
+	return orgs, c.getParsedResponse("GET", fmt.Sprintf("/users/%s/orgs", user), nil, nil, &orgs)
+}
+
+func (c *Client) GetOrg(orgname string) (*Organization, error) {
+	org := new(Organization)
+	return org, c.getParsedResponse("GET", fmt.Sprintf("/orgs/%s", orgname), nil, nil, org)
+}
+
+type CreateOrgOption struct {
+	UserName    string `json:"username" binding:"Required"`
+	FullName    string `json:"full_name"`
+	Description string `json:"description"`
+	Website     string `json:"website"`
+	Location    string `json:"location"`
+}
+
+type EditOrgOption struct {
+	FullName    string `json:"full_name"`
+	Description string `json:"description"`
+	Website     string `json:"website"`
+	Location    string `json:"location"`
+}
+
+func (c *Client) CreateOrg(opt CreateOrgOption) (*Organization, error) {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return nil, err
+	}
+	org := new(Organization)
+	return org, c.getParsedResponse("POST", "/user/orgs", jsonHeader, bytes.NewReader(body), org)
+}
+
+func (c *Client) EditOrg(orgname string, opt EditOrgOption) error {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return err
+	}
+	_, err = c.getResponse("PATCH", fmt.Sprintf("/orgs/%s", orgname), jsonHeader, bytes.NewReader(body))
+	return err
+}