CalendarEvent platforms aren't limited

[Jarno458]

Currently the platform property of openapi/components/requests/CreateCalendarEventRequest.yaml
Allows an array of arbitrary strings, this should probably be limited to only the values vrchat understands

    "platforms": [
        "android",
        "standalonewindows",
        "ios"
    ]

maybe the calendar event type in general should have this limitation applied so also here
openapi/components/schemas/CalendarEvent.yaml