Panel overrides can sometimes be duplicated with autofix enabled

[bderrly]

Given a (truncated) panel overrides seen below (fig 1), running autofix on the panel will result in some of the JSON object being duplicated (fig 2). This is caused by the unmarshaling of the JSON panel into Go objects during the lint phase. When the modified dashboard is marshaled to JSON and used within the conflate library only the properties section of the overrides has been preserved in the modified version. Conflate then sees the full version in the original dashboard panel and thinks, rightly, that there are two distinct objects (one in the original and one in the modified version).

fig. 1, this is extracted from a panel object

"overrides": [
  {
    "__systemRef": "hideSeriesFrom",
    "matcher": {
      "id": "byNames",
      "options": {
        "mode": "exclude",
        "names": ["foo"],
        "prefix": "All except:",
        "readOnly": true
      }
    },
    "properties": [
      {
        "id": "custom.hideFrom",
        "value": {
          "legend": false,
          "tooltip": false,
          "viz": true
        }
      }
    ]
  }
]

fig. 2, the overrides after running lint with autofix enabled

"overrides": [
  {
    "__systemRef": "hideSeriesFrom",
    "matcher": {
      "id": "byNames",
      "options": {
        "mode": "exclude",
        "names": ["foo"],
        "prefix": "All except:",
        "readOnly": true
      }
    },
    "properties": [
      {
        "id": "custom.hideFrom",
        "value": {
          "legend": false,
          "tooltip": false,
          "viz": true
        }
      }
    ]
  },
  {
    "properties": [
      {
        "id": "custom.hideFrom",
        "value": {
          "legend": false,
          "tooltip": false,
          "viz": true
        }
      }
    ]
  }
]