Events API - add ICS export URL to event object

[carrythebanner]

The Events API currently has a shareable property with a full URL to the event on the web.

Example:

{
  "events": [
    {
      "id": "6245",
      "caldaily_id": "9300",
      "title": "Shift to Pedalpalooza Ride",
      ...
      "shareable": "https://shift2bikes.org/calendar/event-9300",
    }
  ]
}

(see API docs)

To export the event to an ICS file (vCalendar format), you have to know the API URL. Currently our front-end client builds the URL itself:

shift-docs/site/themes/s2b_hugo_theme/assets/js/cal/main.js

Line 54 in 6d64d50

value.exportlink = '/api/ics.php?id=' + value.id;

If each event object included its own export URL clients could simply use that as-is, e.g.

{
  "events": [
    {
      "id": "6245",
      "caldaily_id": "9300",
      "title": "Shift to Pedalpalooza Ride",
      ...
      "shareable": "https://shift2bikes.org/calendar/event-9300",
      "export": "https://shift2bikes.org/api/ics.php?id=6245",
    }
  ]
}

(Note that ICS export currently uses the calevent ID aka listing ID, which exports all occurrences.)

See also #735.