add read stats in addition to borrows

Historically, we've only counted borrowing stats and not access to open materials.

openlibrary/plugins/upstream/borrow.py

@@ -158,6 +158,7 @@ def POST(self, key):  # noqa: PLR0915
         response = lending.get_availability_of_ocaid(edition.ocaid)
         availability = response[edition.ocaid] if response else {}
         if availability and availability['status'] == 'open':
+            stats.increment('ol.reads.bookreader')
             raise web.seeother(archive_url)
 
         error_redirect = archive_url