arm-custom-metric-namespace

"criteria": {
    "odata.type": "Microsoft.Azure.Monitor.SingleResourceMultipleMetricCriteria",
    "allOf": [
        {
            "name" : "1st criterion",
            "metricName": "[parameters('metricName')]",
            "metricNamespace": "[parameters('metricNamespace')]",
            "dimensions":[],
            "operator": "[parameters('operator')]",
            "threshold" : "[parameters('threshold')]",
            "timeAggregation": "[parameters('timeAggregation')]"
        }
    ]
}