Ability to set disabled for NestedSelect widget

[mayonnaisecolouredbenz7]

ALL software version info

Software Version Info

panel==1.5.4

Description of expected behavior and the observed behavior

Disabled argument to work with NestedSelect

Complete, minimal, self-contained example code that reproduces the issue

select = pn.widgets.NestedSelect(
    options={
        "GFS": {
            "0.25 deg": ["00Z", "06Z", "12Z", "18Z"],
            "0.5 deg": ["00Z", "12Z"],
            "1 deg": ["00Z", "12Z"],
        },
        "NAME": {
            "12 km": ["00Z", "12Z"],
            "3 km": ["00Z", "12Z"],
        },
    },
    levels=[{'name':"Model","type": pn.widgets.RadioBoxGroup}, "Resolution", "Initialization"],
    disabled = True,
)

• I have made a PR for this