Add support for forum interaction events

[bmtcril]

The default platform forums send several tracking log events. We'd like to capture these for engagement reporting someday. The full list of events is here: https://docs.openedx.org/en/latest/developers/references/internal_data_formats/tracking_logs/student_event_types.html#discussion-forum-events

I think we're particularly interested in the *.viewed, *.created, and *.voted events to start with.

[ziafazal]

@bmtcril I'm trying to find appropriate verbs for these events

edx.forum.thread.created
edx.forum.thread.viewed
edx.forum.thread.edited
edx.forum.thread.deleted

I have found these existing verbs. are these verbs are fine or we should create our own in open edx profile?
posted for edx.forum.thread.created
viewed for edx.forum.thread.viewed
edited for edx.forum.thread.edited
deleted for edx.forum.thread.deleted

[bmtcril]

@ziafazal those seem reasonable to me!