New Experiment spinup-1950

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Adding the following new data.

{
    "id": "spinup-1950",
    "type": [
        "wcrp:experiment",
        "cmip7"
    ],
    "activity": [
        "HighResMIP2"
    ],
    "description": "This experiment is designed to provide a multidecadal spinup for coupled model simulations. Its final output will serve as initial conditions for the control-1950, hist-1950, and highres-4xCO2 scenarios. The setup follows the same design as HighResMIP1, typically run for 50 years starting from the initial conditions.  For solar and ozone forcing, we suggest using an 11-year climatology centered on 1950 to average the solar cycle. For greenhouse gases (GHG), concentrations can be set to 1950 values as defined in CMIP. A 10-year mean around 1950 (e.g., 1946\u20131955 or 1950\u20131959) is recommended for aerosols and volcanic forcing.  For further details, please refer to: Roberts et al. (2025). High-Resolution Model Intercomparison Project phase 2 (HighResMIP2) towards CMIP7. Geoscientific Model Development, 18, 1307\u20131332.",
    "label": "spinup-1950",
    "long-label": "Coupled control spinup-1950",
    "minimum-number-of-years": "50",
    "model-realms": [
        {
            "id": "aogcm",
            "is-required": true
        },
        {
            "id": "bgc",
            "is-required": false
        },
        {
            "id": "chem",
            "is-required": false
        },
        {
            "id": "aer",
            "is-required": false
        }
    ],
    "parent-experiment": [
        "none"
    ],
    "start-date": "none",
    "sub-experiment": "none",
    "tier": "1"
}

Resolves #69