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_email.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"
+)
+
+type Email struct {
+	Email    string `json:"email"`
+	Verified bool   `json:"verified"`
+	Primary  bool   `json:"primary"`
+}
+
+func (c *Client) ListEmails() ([]*Email, error) {
+	emails := make([]*Email, 0, 3)
+	return emails, c.getParsedResponse("GET", "/user/emails", nil, nil, &emails)
+}
+
+type CreateEmailOption struct {
+	Emails []string `json:"emails"`
+}
+
+func (c *Client) AddEmail(opt CreateEmailOption) ([]*Email, error) {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return nil, err
+	}
+	emails := make([]*Email, 0, 3)
+	return emails, c.getParsedResponse("POST", "/user/emails", jsonHeader, bytes.NewReader(body), emails)
+}
+
+func (c *Client) DeleteEmail(opt CreateEmailOption) error {
+	body, err := json.Marshal(&opt)
+	if err != nil {
+		return err
+	}
+	_, err = c.getResponse("DELETE", "/user/emails", jsonHeader, bytes.NewReader(body))
+	return err
+}