New Experiment abrupt-2xCO2

[github-actions]

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Adding the following new data.

{
    "id": "abrupt-2xco2",
    "type": [
        "wcrp:experiment",
        "cmip7"
    ],
    "activity": [
        "CFMIP"
    ],
    "branch-date": "none",
    "description": "Identical to the `piControl` DECK experiment but with a step change to 2xCO2 concentration from its pre-industrial value, held constant for the duration of the run.  Reference: [Webb et al., 2017](https://doi.org/10.5194/gmd-10-359-2017)",
    "label": "abrupt-2xCO2",
    "long-label": "Abrupt doubling of CO2",
    "minimum-number-of-years": "300",
    "model-realms": [
        {
            "id": "aogcm",
            "is-required": true
        },
        {
            "id": "aer",
            "is-required": false
        },
        {
            "id": "bgc",
            "is-required": false
        },
        {
            "id": "chem",
            "is-required": false
        }
    ],
    "parent-experiment": [
        "piControl"
    ],
    "start-date": "_No response_",
    "sub-experiment": "none",
    "tier": "1"
}

Resolves #39