directly connect to frontend

The STORAGE_USERS_DATA_GATEWAY_URL env var is used in the `tokens` `datagateway_endpoint` reva configuration. That `DataGatewayEndpoint` is used by the decomposedfs driver to create urls:
```go
// URL returns a url to download an upload
func (session *DecomposedFsSession) URL(_ context.Context) (string, error) {
       // [ ... ]
	return joinurl(session.store.tknopts.DataGatewayEndpoint, tkn), nil
}
```
As the comment points out this URL is internally used when emitting events. Either in:
```go
func (session *DecomposedFsSession) FinishUploadDecomposed(ctx context.Context) error {
                // [ ... ]
		s, err := session.URL(ctx)
		if err != nil {
			return err
		}

		var iu *userpb.User
		if utils.ExistsInOpaque(u.Opaque, "impersonating-user") {
			iu = &userpb.User{}
			if err := utils.ReadJSONFromOpaque(u.Opaque, "impersonating-user", iu); err != nil {
				return err
			}
		}

		if err := events.Publish(ctx, session.store.pub, events.BytesReceived{
			UploadID:          session.ID(),
			URL:               s,
```

or in
```go

// Postprocessing starts the postprocessing result collector
func (fs *Decomposedfs) Postprocessing(ch <-chan events.Event) {
                        // [ ... ]
			s, err := session.URL(ctx)
			if err != nil {
				sublog.Error().Err(err).Msg("could not create url")
				continue
			}

			metrics.UploadSessionsRestarted.Inc()

			// restart postprocessing
			if err := events.Publish(ctx, fs.stream, events.BytesReceived{
				UploadID:      session.ID(),
				URL:           s,
```

So, we do not need to go throught the proxy here.

services/storage-users/pkg/config/defaults/defaultconfig.go

@@ -86,7 +86,7 @@ func DefaultConfig() *config.Config {
 		},
 		Reva:                    shared.DefaultRevaConfig(),
 		DataServerURL:           "http://localhost:9158/data",
-		DataGatewayURL:          "https://localhost:9200/data",
+		DataGatewayURL:          "http://localhost:9140/data",
 		RevaGatewayGRPCAddr:     "127.0.0.1:9142",
 		TransferExpires:         86400,
 		UploadExpiration:        24 * 60 * 60,