In Salesforce, I would like to add a custom activity to a contact's or opportunity's Activity timeline. For example, in the timeline below, we see an outgoing email, and two tasks:
As far as I can discover so far, this activities list is made of of Events and Tasks, with an "event" essentially a meeting or similar, which appears on the calendar, and a "task" being a type of to-do item.
I would like to add something completely custom, with its own fields/text, and preferably with its own icon. Is it possible to do this via the REST API?