docs: More html/docs changes from libvirt.h.in split

docs: More html/docs changes from libvirt.h.in split

This changes the display from:

libvirt-storage: APIs for management of storages

to

libvirt-storage: APIs for management of storage pools and volumes

In making that change I expected my build tree html output to be
regenerated; however, it wasn't because the dependency for the separated
libvirt-storage.h wasn't there.  It was only present for libvirt.h.in

So I added each in the order displayed on the docs/html/index.html page