Private notes attached to calendar events for meeting prep

Add private notes attached to calendar events, for rough personal meeting preparation such as a mini agenda of talking points that is not shared with the other person and is not a full note-taker document. The current workaround is creating a task next to every event at the same time as the calendar event, naming it something like “Mike/<other person> agenda” and putting the private agenda/thoughts/notes in the task description; with dozens of meetings per week these agenda notes pile up and clutter the task list. Alternatives already discarded: linking to a Google Doc from the calendar event (tedious, and a whole Google Doc for 2-4 partially-written sentences feels heavy, plus the note should stay directly on the calendar and private when a meeting is scheduled a week or two in advance), and privately editing calendar events 'locally' (complicated later when updating the event time/date — private notes have accidentally been shared by updating the event time and syncing both the new time and the private notes without realizing it). Timeslot notes: while less important, notes on time slots would also have some value — when several tasks are grouped together, a little workspace of all thoughts on the tasks in one place would be nicer than notes spread across each individual task; the customer is less convinced this is required because specific use cases are hard to describe, but would likely end up using it. Not critical to the main request.