Is your feature request related to a problem?

After implementing #6105, #6106 and #6127, events in the event calendar view can be colored based on their category, location and keywords. It would be useful to filter which events appear in the calendar based on which legend items are checked.

Describe the solution you'd like

Make it possible to check which legend items are active in the calendar. For this, we can turn the colored squares left of each item in the legend into a checkbox (similar to how Google Calendar allows filtering events by calendar). By default, all the items in the legend should be checked. Clicking on the colored squared toggles if the events associated with that item appear or not in the calendar.

Additional context

This feature request comes inspired by Perimeter Institute's in-house developed calendar view: