Add annotations in grafana for each deployment

[sduranc]

• [x] 1. For each successful deployment there should be an annotation in Grafana to display the timestamp it happened
• [x] 2. Define an initial set of labels, so that annotations can be filtered out later by app, team, etc

[sduranc]

For 1. we're relying on the notifications controller from Flux, as initial solution

[sduranc]

Labels will be initially these:

      "eventMetadata" = {
        "env" = "${var.environment}"
        "cluster" = "${azurerm_kubernetes_cluster.aks.name}"
        "app" = "${var.app}"
      }