Support additional properties on Collection class

[aaronpowell]

While fixing #1361 I noticed that there is a type I'd not seen before in the JSON back from the IWC API, special.

Looking at the JSON from the API I saw it is this:

    {
        "id": 37,
        "name": "Free Household Chemcial Cleanout & e-waste drop off event",
        "description": "<p>Sort through and declutter your homes, garages and sheds of chemicals and broken electronics and dispose of them correctly and for free at the Household Chemical Cleanout &amp; e-waste event. These items cannot be disposed of in our garbage bins due to their hazardous nature but can be dropped off for free. The event is on Saturday 4 November, 9am-3:30pm at the rear of the Inner West Council Works Depot, 15-17 Unwins Bridge Road, St Peters. (Please note entry via the rear of the depot, parallel to the railway tracks through Bolton Street). Exit is via the Unwins Bridge Road gate as a left hand turn only.<br>Many items are accepted like paints, pesticides, gas cylinders, herbicides, fire extinguishers, gas cylinders, smoke alarms, TVs, computers, keyboards and much more.&nbsp;</p><p>More information can be found at <a target=\"_blank\" rel=\"noopener noreferrer\" href=\"http://www.innerwest.nsw.gov.au/dropoff\">www.innerwest.nsw.gov.au/dropoff</a>.<br>Chemicals will be safely disposed and electronics will be recycled.<br>Avoid the morning queues, if possible, and visit around noon.<br>Please note the CRC is located at the same location and will be closed on the day. All items accepted at the CRC is also accepted at this event however the opening time is from 9am-3:30pm.<br>Help take a step closer to zero waste.</p>",
        "color": "#A72DFC",
        "textColor": "#A72DFC",
        "borderColor": "#000",
        "start": "2023-11-04",
        "event_type": "special"
    }

The additional information would be good to make available to HA. Does the Collection class support arbitrary properties? If not, can it be extended to support them?

[5ila5]

This is currently not supported