fix(telemetry): point template variables at the datasource variable

Sixteen template variables named a datasource by the literal uid "prometheus"
or "loki". Neither exists on the Grafana instance, so those variables resolved
to nothing and their pickers offered only All.

That also broke the panels. With an empty variable the selector becomes
job_type=~"" rather than job_type=~".*", which matches no series, so the
Current Job Latency gauge had no data and its renderer raised the plugin error
banner on every refresh.

Every working dashboard already references ${DS_PROMETHEUS} or ${DS_LOKI},
which the dashboard declares in templating.list. These now match.

job-queue 6, ledger-data-sync 5, log-derived-insights 3, overlay-traffic-detail 2.

docker/telemetry/grafana/dashboards/job-queue.json

@@ -621,7 +621,7 @@
         "query": "label_values(service_name)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -641,7 +641,7 @@
         "query": "label_values(deployment_environment)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -661,7 +661,7 @@
         "query": "label_values(xrpl_network_type)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -741,7 +741,7 @@
         "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -761,7 +761,7 @@
         "query": "label_values(job_queued_total, job_type)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -781,7 +781,7 @@
         "query": "label_values(job_queued_total, handler)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",

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

@@ -2365,7 +2365,7 @@
         "query": "label_values(service_name)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -2385,7 +2385,7 @@
         "query": "label_values(deployment_environment)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -2405,7 +2405,7 @@
         "query": "label_values(xrpl_network_type)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -2485,7 +2485,7 @@
         "query": "label_values(target_info, service_instance_id)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -2505,7 +2505,7 @@
         "query": "label_values(job_queued_total, handler)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",

docker/telemetry/grafana/dashboards/log-derived-insights.json

@@ -90,7 +90,7 @@
         "query": "label_values(service_name)",
         "datasource": {
           "type": "loki",
-          "uid": "loki"
+          "uid": "${DS_LOKI}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -110,7 +110,7 @@
         "query": "label_values({service_name=\"xrpld\"}, deployment_environment)",
         "datasource": {
           "type": "loki",
-          "uid": "loki"
+          "uid": "${DS_LOKI}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -130,7 +130,7 @@
         "query": "label_values({service_name=\"xrpld\"}, service_instance_id)",
         "datasource": {
           "type": "loki",
-          "uid": "loki"
+          "uid": "${DS_LOKI}"
         },
         "includeAll": true,
         "allValue": ".*",

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

@@ -1135,7 +1135,7 @@
         "query": "label_values(getobject_lookups_total, result)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",
@@ -1155,7 +1155,7 @@
         "query": "label_values(getobject_rejected_total, reason)",
         "datasource": {
           "type": "prometheus",
-          "uid": "prometheus"
+          "uid": "${DS_PROMETHEUS}"
         },
         "includeAll": true,
         "allValue": ".*",