Separate feature discovery and creation of feature labels. Generalize
the feature discovery so that block devices can be matched in custom
label rules in a similar fashion as pci and usb devices. This extends
the discovery to other block queue attributes than 'rotational': now we
also detect 'dax', 'nr_zones' and 'zoned'.

Labels created by the storage feature source are unchanged. The new
features being detected are available in custom rules only.

Example custom rules:

  - name: "my block rule 1"
    labels:
      my-block-feature-1: "true"
    matchFeatures:
      - feature: storage.block
          "rotational": {op: In, value: ["0"]}

  - name: "my block rule 2"
    labels:
      my-block-feature-2: "true"
    matchFeatures:
      - feature: storage.block
          "zoned": {op: In, value: [“host-aware”, “host-managed”]}

Also, add minimalist unit test.