How to give a regex in source_labels in promethues?

Grafana Configuration
1

I have a metric like this kube_deployment_labels{label_graph_v1="graph_v1", label_graph_test="graph_test"}

I want to transform it to kube_deployment_labels{label_graph_v1="graph_v1", label_graph_test="graph_test", graph_names="graph_test,graph_v1}

What i want to be able to configure something like this

relabel_configs:
- source_labels: ["label_graph.*"]
  separator: ","
  target_label: "graph_names"
  action: "replace"

But source_labels doesnt seem to accept regex and if i use labelmap, it becomes a one to one mapping and i am not able to club many labels together.

My goal is to be able to specify a legend like {{graph_names}} in the LegendFormat in the grafana dashboard.

Like this

So

Is there any way for me to club the label_values based on a regex?
Is there any way to display only the labels names/values in grafana dashboard, because i can choose to drop labels based on a regex.