selftests: tc-testing: Add matchJSON to tdc

This allows the use of a matchJSON field in tests to match
against JSON output from the command under test, if that
command outputs JSON.

You specify what you want to match against as a JSON array
or object in the test's matchJSON field. You can leave out
any fields you don't want to match against that are present
in the output and they will be skipped.

An example matchJSON value would look like this:

"matchJSON": [
  {
    "Value": {
      "neighIP": {
        "family": 4,
        "addr": "AQIDBA==",
        "width": 32
      },
      "nsflags": 142,
      "ncflags": 0,
      "LLADDR": "ESIzRFVm"
    }
  }
]

The real output from the command under test might have some
extra fields that we don't care about for matching, and
since we didn't include them in our matchJSON value, those
fields will not be attempted to be matched. If everything
we included above has the same values as the real command
output, the test will pass.

The matchJSON field's type must be the same as the command
output's type, otherwise the test will fail. So if the
command outputs an array, then the value of matchJSON must
also be an array.

If matchJSON is an array, it must not contain more elements
than the command output's array, otherwise the test will
fail.

Signed-off-by: Jeremy Carter <jeremy@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20221024111603.2185410-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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