feature: add booking URLs in some way

[francojreyes]

It's possible to link directly to a booking URL for libcal (e.g. https://unswlibrary-bookings.libcal.com/space/45757) but it didn't really fit in to the schema in any way since the ID is different, and there is no equivalent for NSS, so it wasn't included.

It's definitely worth exploring though, since being taken straight to the room booking page is a lot more useful than the current link to the overall library booking page.