taken mostly from PVE, with adaption to how PBS does things.
Main difference is that we do not have a resource store singleton
here which we can use, but for datastores we can already use the
always present datastore-list store. Register it to the store manager
with a "storeId" property (vs. our internal storeid one).
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>