added MarkAreaDataItem

[mwlazlo]

Description

Previous implementation does not support markArea very well. It would render like this:

  "markArea": {
    "data": [
      {
        "name": "ref",
        "yAxis": 7023
      },
      {
        "yAxis": 6996
      }
    ]
  }

When was was needed was this:

  "markArea": {
    "data": [
      [
        {
          "name": "ref",
          "yAxis": 7023
        },
        {
          "yAxis": 6996
        }
      ]
    ]
  }

This PR tries to implement a more flexible data structure, allowing the user to create configurations closer to the documentation: https://echarts.apache.org/en/option.html#series-candlestick.markArea.data

Type of change

• Bug fix (Non-breaking change which fixes an issue)
• New feature (Non-breaking change which adds functionality)
• Breaking change (Would cause existing functionality to not work as expected)
• Others

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Examples:

Are you willing to submit a PR on go-echarts/Examples?

• Yes, I am willing to submit a PR on Examples!