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_team.go

@@ -0,0 +1,25 @@
+// Copyright 2016 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"
+
+type Team struct {
+	ID          int64  `json:"id"`
+	Name        string `json:"name"`
+	Description string `json:"description"`
+	Permission  string `json:"permission"`
+}
+
+type CreateTeamOption struct {
+	Name        string `json:"name" binding:"Required;AlphaDashDot;MaxSize(30)"`
+	Description string `json:"description" binding:"MaxSize(255)"`
+	Permission  string `json:"permission"`
+}
+
+func (c *Client) ListTeams(name string) ([]*Team, error) {
+	teams := make([]*Team, 0, 5)
+	return teams, c.getParsedResponse("GET", fmt.Sprintf("/orgs/%s/teams", name), nil, nil, &teams)
+}