feat(cmds): add dag diff

[schomatis]

IPFS_CMD=cmd/ipfs/ipfs
NODE_BEFORE=QmUNLLsPACCz1vLxQVkXqqLX5R1X345qqfHbsf67hvA3Nn # empty dir
NODE_AFTER=QmQPeNsJPyVWPFDVHb77w8G42Fvo15z4bG2X8D2GhfbSXc # ipfs init dir
$IPFS_CMD dag diff $NODE_BEFORE $NODE_AFTER

[
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmQy6xmJhrcC5QLboAcGFcAE1tC8CrwDVkrHdEYJkLscrQ"
      },
      "Name": "about",
      "Tsize": 1692
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmYCvbfNbCwFR45HiNP45rwJgvatpiW38D961L5qAhUM5Y"
      },
      "Name": "contact",
      "Tsize": 200
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmU5k7ter3RdjZXu3sHghsga1UQtrztnQxmTL22nPnsu3g"
      },
      "Name": "help",
      "Tsize": 322
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmejvEPop4D7YUadeGqYWmZxHhLc4JBUCzJJHWMzdcMe2y"
      },
      "Name": "ping",
      "Tsize": 12
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmQGiYLVAdSHJQKYFRTJZMG4BXBHqKperaZtyKGmCRLmsF"
      },
      "Name": "quick-start",
      "Tsize": 1692
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmPZ9gcCEpqKTo6aq61g2nXGUhM4iCL3ewB6LDXZCtioEB"
      },
      "Name": "readme",
      "Tsize": 1102
    }
  },
  {
    "op": "add",
    "path": "/Links/-",
    "value": {
      "Hash": {
        "/": "QmQ5vhrL7uv6tuoN9KeVBwd4PwfQkXdVVmDLUZuTNxqgvm"
      },
      "Name": "security-notes",
      "Tsize": 1173
    }
  }
]

Toward #4801.

[schomatis]

@lidel Thanks for the pointers. Ready for another round of review.

[BigLep]

2022-10-04 Kubo standup conversation: this requires deeper thought because it has impact on other commands. When we pick this up, it will be good to engage with it during the IPLD community call.