Support Proxy protocol (#12527)

This PR adds functionality to allow Gitea to sit behind an
HAProxy and HAProxy protocolled connections directly.

Fix #7508

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/ssh/ssh_graceful.go

@@ -17,7 +17,7 @@ func listen(server *ssh.Server) {
 	gracefulServer.PerWriteTimeout = setting.SSH.PerWriteTimeout
 	gracefulServer.PerWritePerKbTimeout = setting.SSH.PerWritePerKbTimeout
 
-	err := gracefulServer.ListenAndServe(server.Serve)
+	err := gracefulServer.ListenAndServe(server.Serve, setting.SSH.UseProxyProtocol)
 	if err != nil {
 		select {
 		case <-graceful.GetManager().IsShutdown():