enable_virtual_node_label config not work

[chenlujjj]

Describe the bug

I set enable_virtual_node_label: true in the service graph config, but the metrics still don't have virtual_node label

To Reproduce

1. Setup a distributed tempo
2. Enable service graph metrics generator and remote write metrics to TSDB
3. Set enable_virtual_node_label: true in the service graph config
4. Query metrics via traces_service_graph_request_total{connection_type="virtual_node"}

Expected behavior

The metrics should have virtual_node label as the doc (https://grafana.com/docs/tempo/latest/metrics-generator/service_graphs/#activate-enable_virtual_node_label) said

Environment:

• Infrastructure: [Kubernetes]
• Deployment tool: [helm]

Additional Context