Fix webhooks to use proxy from environment (#8116)

models/webhook.go

@@ -973,6 +973,7 @@ func InitDeliverHooks() {
 	webhookHTTPClient = &http.Client{
 		Transport: &http.Transport{
 			TLSClientConfig: &tls.Config{InsecureSkipVerify: setting.Webhook.SkipTLSVerify},
+			Proxy:           http.ProxyFromEnvironment,
 			Dial: func(netw, addr string) (net.Conn, error) {
 				conn, err := net.DialTimeout(netw, addr, timeout)
 				if err != nil {