Clarity about which events are event-bus capable and the differences between bus and non-bus events

[mariajgrimaldi]

Description

Some comments I've gathered from the community survey on the challenges/suggestions section:

Finding a comprehensive list of events/filters (especially those outside of edx-platform) is challenging, and they are not all well documented. I added autodoc support for events, but there is probably more work to be done there.
More clarity about which events are event-bus capable and the differences between bus and non-bus events would also be great.