[nancy] Add metrics info for PDU

data/grid5000/sites/nancy/pdus/gros-wattmetre1.json

 {
   "ip": "172.16.79.18",
+  "metrics": [
+    {
+      "description": "Power consumption per outlet reported by wattmetre, in watt",
+      "name": "wattmetre_power_watt",
+      "optional_period": 20,
+      "period": 1000,
+      "source": {
+        "protocol": "wattmetre"
+      }
+    }
+  ],
   "model": "",
   "ports": {
     "0": "gros-1",

data/grid5000/sites/nancy/pdus/gros-wattmetre2.json

 {
   "ip": "172.16.79.18",
+  "metrics": [
+    {
+      "description": "Power consumption per outlet reported by wattmetre, in watt",
+      "name": "wattmetre_power_watt",
+      "optional_period": 20,
+      "period": 1000,
+      "source": {
+        "protocol": "wattmetre"
+      }
+    }
+  ],
   "model": "",
   "ports": {
     "0": "gros-71",

data/grid5000/sites/nancy/pdus/gros-wattmetre3.json

 {
   "ip": "172.16.79.18",
+  "metrics": [
+    {
+      "description": "Power consumption per outlet reported by wattmetre, in watt",
+      "name": "wattmetre_power_watt",
+      "optional_period": 20,
+      "period": 1000,
+      "source": {
+        "protocol": "wattmetre"
+      }
+    }
+  ],
   "model": "",
   "ports": {
     "0": "gros-113",

input/grid5000/sites/nancy/pdus.yaml

@@ -190,6 +190,14 @@ pdus:
             unit: W
             www:
               url: "http://wattmetre.nancy.grid5000.fr/GetWatts-json.php"
+    metrics:
+    - name: wattmetre_power_watt
+      description: Power consumption per outlet reported by wattmetre, in watt
+      period: 1000
+      optional_period: 20
+      source:
+        protocol: wattmetre
+
   gros-wattmetre2:
     vendor: OmegaWatt
     model: ''
@@ -203,6 +211,14 @@ pdus:
             unit: W
             www:
               url: "http://wattmetre.nancy.grid5000.fr/GetWatts-json.php"
+    metrics:
+    - name: wattmetre_power_watt
+      description: Power consumption per outlet reported by wattmetre, in watt
+      period: 1000
+      optional_period: 20
+      source:
+        protocol: wattmetre
+
   gros-wattmetre3:
     vendor: OmegaWatt
     model: ''
@@ -216,3 +232,10 @@ pdus:
             unit: W
             www:
               url: "http://wattmetre.nancy.grid5000.fr/GetWatts-json.php"
+    metrics:
+    - name: wattmetre_power_watt
+      description: Power consumption per outlet reported by wattmetre, in watt
+      period: 1000
+      optional_period: 20
+      source:
+        protocol: wattmetre