Add support of matchLabels and matchExpressions for namespaceSelector

[dmgtn]

Instead of adding support for wildcards, as is described in #20, let we better add something like this:

  "onKubernetesEvent": [
    {
      "name": "Monitor labeled pods in cache tier",
      "kind": "Pod",

      "namespace": {
        "matchLabels": {                          # NEW
          "myLabel": "myLabelValue",              # NEW
          "someKey": "someValue",                 # NEW
          ...                                     # NEW
        },                                        # NEW
        "matchExpressions": [                     # NEW
          {                                       # NEW
            "key": "tier",                        # NEW
            "operation": "In",                    # NEW
            "values": ["cache"],                  # NEW
          },                                      # NEW
      },
    }
  ]

Concepts of matchLabels and matchExpressions are widely used throughout Kubernetes API, in contradiction to wildcards.