fix(unpoller): Prometheus dashboards (#27994)

The unpoller dashboards can't be loaded in Prometheus with the error
"Failed to upgrade legacy queries"

The panels uses the ${DS_PROMETHEUS} variable which is not defined in
the dashboards

**⚙️ Type of change**

- [ ] ⚙️ Feature/App addition
- [x] 🪛 Bugfix
- [ ] ⚠️ Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] 🔃 Refactor of current code

**🧪 How Has This Been Tested?**
I installed the chart with the new dashboards and they work

charts/stable/unpoller/Chart.yaml

@@ -34,4 +34,4 @@ sources:
   - https://github.com/truecharts/charts/tree/master/charts/stable/unpoller
   - https://github.com/unifi-poller/unifi-poller
 type: application
-version: 12.2.0
+version: 12.2.1

charts/stable/unpoller/dashboards/UAP.json

@@ -3512,6 +3512,13 @@
     "tags": ["unifi", "uap", "unifi-poller"],
     "templating": {
         "list": [
+            {
+                "hide": 2,
+                "name": "DS_PROMETHEUS",
+                "query": "Prometheus",
+                "skipUrlSync": false,
+                "type": "constant"
+            },
             {
                 "allValue": ".*",
                 "current": {},

charts/stable/unpoller/dashboards/USG.json

@@ -2362,6 +2362,13 @@
     "tags": ["unifi", "unifi-poller", "usg"],
     "templating": {
         "list": [
+            {
+                "hide": 2,
+                "name": "DS_PROMETHEUS",
+                "query": "Prometheus",
+                "skipUrlSync": false,
+                "type": "constant"
+            },
             {
                 "allValue": ".*",
                 "current": {},

charts/stable/unpoller/dashboards/USW.json

@@ -2649,6 +2649,13 @@
     "tags": ["unifi", "usw", "unifi-poller"],
     "templating": {
         "list": [
+            {
+                "hide": 2,
+                "name": "DS_PROMETHEUS",
+                "query": "Prometheus",
+                "skipUrlSync": false,
+                "type": "constant"
+            },
             {
                 "allValue": ".*",
                 "current": {},

charts/stable/unpoller/dashboards/clients.json

@@ -2958,6 +2958,13 @@
     "tags": ["unifi", "unifi-poller"],
     "templating": {
         "list": [
+            {
+                "hide": 2,
+                "name": "DS_PROMETHEUS",
+                "query": "Prometheus",
+                "skipUrlSync": false,
+                "type": "constant"
+            },
             {
                 "allValue": null,
                 "current": {},

charts/stable/unpoller/dashboards/network.json

@@ -1352,6 +1352,13 @@
     "tags": ["unifi", "unifi-poller"],
     "templating": {
         "list": [
+            {
+                "hide": 2,
+                "name": "DS_PROMETHEUS",
+                "query": "Prometheus",
+                "skipUrlSync": false,
+                "type": "constant"
+            },
             {
                 "allValue": null,
                 "current": {},