Add proxy settings and support for migration and webhook (#16704)

* Add proxy settings and support for migration and webhook

* Fix default value

* Add newline for example ini

* Add lfs proxy support

* Fix lint

* Follow @zeripath's review

* Fix git clone

* Fix test

* missgin http requests for proxy

* use empty

Co-authored-by: zeripath <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>

modules/setting/proxy.go

@@ -0,0 +1,40 @@
+// Copyright 2021 The Gitea 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 setting
+
+import (
+	"net/url"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+var (
+	// Proxy settings
+	Proxy = struct {
+		Enabled       bool
+		ProxyURL      string
+		ProxyURLFixed *url.URL
+		ProxyHosts    []string
+	}{
+		Enabled:    false,
+		ProxyURL:   "",
+		ProxyHosts: []string{},
+	}
+)
+
+func newProxyService() {
+	sec := Cfg.Section("proxy")
+	Proxy.Enabled = sec.Key("PROXY_ENABLED").MustBool(false)
+	Proxy.ProxyURL = sec.Key("PROXY_URL").MustString("")
+	if Proxy.ProxyURL != "" {
+		var err error
+		Proxy.ProxyURLFixed, err = url.Parse(Proxy.ProxyURL)
+		if err != nil {
+			log.Error("Global PROXY_URL is not valid")
+			Proxy.ProxyURL = ""
+		}
+	}
+	Proxy.ProxyHosts = sec.Key("PROXY_HOSTS").Strings(",")
+}