For the default UK grid intensity API - 'very high' needs to be supported

[mrchrisadams]

This library when querying the UK grid intensity API assumes the value can be low, medium or high.

This looks like an assumption we need to update, based on the figure here:

{
  "data": [
    {
      "from": "2024-01-12T12:00Z",
      "to": "2024-01-12T12:30Z",
      "intensity": {
        "forecast": 284,
        "actual": 279,
        "index": "very high"
      }
    }
  ]
}

Why did we not see this before? It might be that it hasn't been this cold in a while, or that we just didn't see it before on branch.

The code in question is at the link below.

https://github.com/thegreenwebfoundation/grid-intensity/blob/main/src/index.test.js#L108-L145

The quickest fix would be to 'cast' a very high result to high.

The longer term fix would probably be to include this functionality in CO2.js, because only querying the UK grid intensity API has plent of shortcomings if you are not in the UK.

[mrchrisadams]

LOL, now later in the year on a day where it's been particularly windy and sunny in the uk, we've had 'very low' which we need to cast to 'low' for the purposes of any branch-y designs using this libary.