This patch adds 'article' to the list of triggers available for
tracking patron activity.
Test plan
1) Select 'Placing an article request
TrackPatronLastActivityTriggers system preference
2) As a staff member, place a hold on any item for a test user
3) Confirm that the borrowers.lastseen field is updated for that
test borrower
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
