nfd-master: handle multiple NodeFeature objects

[marquiz]

Implement handling of multiple NodeFeature objects by merging all objects (targeting a certain node) into one before processing the data. This patch implements MergeInto() methods for all required data types.

With support for multiple NodeFeature objects per node, The "nfd api workflow" can be easily demonstrated and tested from the command line. Creating the folloiwing object (assuming node-n exists in the cluster):

    apiVersion: nfd.k8s-sigs.io/v1alpha1
    kind: NodeFeature
    metadata:
      labels:
        nfd.node.kubernetes.io/node-name: node-n
      name: my-features-for-node-n
    spec:
      # Features for NodeFeatureRule matching
      features:
        flags:
          vendor.domain-a:
            elements:
              feature-x: {}
        attributes:
          vendor.domain-b:
            elements:
              feature-y: "foo"
              feature-z: "123"
        instances:
          vendor.domain-c:
            elements:
            - attributes:
                name: "elem-1"
                vendor: "acme"
            - attributes:
                name: "elem-2"
                vendor: "acme"
      # Labels to be created
      labels:
        vendor-feature.enabled: "true"
        vendor-setting.value: "100"

will create two feature labes:

    feature.node.kubernetes.io/vendor-feature.enabled: "true"
    feature.node.kubernetes.io/vendor-setting.value: "100"

In addition it will advertise hidden/raw features that can be used for custom rules in NodeFeatureRule objects. Now, creating a NodeFeatureRule object:

    apiVersion: nfd.k8s-sigs.io/v1alpha1
    kind: NodeFeatureRule
    metadata:
      name: my-rule
    spec:
      rules:
        - name: "my feature rule" labels: "my-feature": "true" matchFeatures: - feature: vendor.domain-a matchExpressions: feature-x: {op: Exists} - feature: vendor.domain-c matchExpressions: vendor: {op: In, value: ["acme"]}

will match the features in the NodeFeature object above and cause one more label to be created:

    feature.node.kubernetes.io/my-feature: "true"

Split out from #903

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[k8s-triage-robot]

Unknown CLA label state. Rechecking for CLA labels.

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[marquiz]

Rebased.

[ArangoGutierrez]

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 97077f771c38e9b19184bc257281d572c0844b90

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ArangoGutierrez, marquiz

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