Use azure metrics on OS dashboards

It's required to use specific azure metrics in formulas on OS dashboards.

Also it's required to make sure that adopted azure metrics are correctly worked in existent formulas on OS dashbaords.

Early testing steps:

• Add a generic node

  $ curl -s -u admin:admin -d '{"address": "1.2.3.4", "custom_labels": {"custom_label": "for_an_azure_node"}, "node_name": "azure_node1"}' http://172.17.0.2/v1/inventory/Nodes/AddGeneric
  {
    "generic": {
      "node_id": "/node_id/2a35f820-9b76-4205-93cd-51f9f70ae608",
      "node_name": "azure_node1",
      "address": "1.2.3.4",
      "custom_labels": {
        "custom_label": "for_an_azure_node"
      }
    }
  

• run azure exporter (details in ticket https://jira.percona.com/browse/PMM-7678"
• add external monitoring

  $ pmm-admin add external --listen-port=9276 --service-name="MyAzureNode" --service-node-id="/node_id/2a35f820-9b76-4205-93cd-51f9f70ae608"
  External Service added.
  Service ID  : /service_id/35e6a54c-2a4f-4e2d-ad6e-83681f7b1305
  Service name: MyAzureNode
  Group       : external
  

• Dashboard Elements for checking
  1. Memory Available
  2. Disk Space
  3. CPU Usage
  4. Min Space Available
  5. Network Traffic
  6. Network Utilization Hourly