Use different user-agent for twitter links (#16210)

services/httpservice/client.go

@@ -136,7 +136,7 @@ func dialContextFilter(dial DialContextFunction, allowHost func(host string) boo
 	}
 }
 
-func NewTransport(enableInsecureConnections bool, allowHost func(host string) bool, allowIP func(ip net.IP) bool) http.RoundTripper {
+func NewTransport(enableInsecureConnections bool, allowHost func(host string) bool, allowIP func(ip net.IP) bool) *MattermostTransport {
 	dialContext := (&net.Dialer{
 		Timeout:   ConnectTimeout,
 		KeepAlive: 30 * time.Second,