fix(telemetry): seed $node dashboard filter from target_info

Seed the $node template variable from target_info instead of a
signal-specific metric. Signal metrics only list nodes that emit that
specific signal, so nodes (e.g. Alloy-collected ones) were missing from
the dropdown and every panel. target_info is emitted for every node, so
all nodes are always selectable. Panels already filter on
service_instance_id=~"$node", so no panel changes are needed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docker/telemetry/grafana/dashboards/ledger-data-sync.json

@@ -561,7 +561,7 @@
         "label": "Node",
         "description": "Filter by rippled node (service.instance.id)",
         "type": "query",
-        "query": "label_values(ledger_data_get_bytes_in, service_instance_id)",
+        "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
           "uid": "prometheus"

docker/telemetry/grafana/dashboards/network-traffic.json

@@ -839,7 +839,7 @@
         "label": "Node",
         "description": "Filter by rippled node (service.instance.id)",
         "type": "query",
-        "query": "label_values(peer_finder_active_inbound_peers, service_instance_id)",
+        "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
           "uid": "prometheus"

docker/telemetry/grafana/dashboards/node-health.json

@@ -964,7 +964,7 @@
         "label": "Node",
         "description": "Filter by rippled node (service.instance.id)",
         "type": "query",
-        "query": "label_values(ledgermaster_validated_ledger_age, service_instance_id)",
+        "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
           "uid": "prometheus"

docker/telemetry/grafana/dashboards/overlay-traffic-detail.json

@@ -621,7 +621,7 @@
         "label": "Node",
         "description": "Filter by rippled node (service.instance.id)",
         "type": "query",
-        "query": "label_values(squelch_messages_in, service_instance_id)",
+        "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
           "uid": "prometheus"

docker/telemetry/grafana/dashboards/rpc-pathfinding.json

@@ -682,7 +682,7 @@
         "label": "Node",
         "description": "Filter by rippled node (service.instance.id)",
         "type": "query",
-        "query": "label_values(rpc_requests_total, service_instance_id)",
+        "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
           "uid": "prometheus"