LP#1873048: add scoped retrieve perm for booking resource types

LP#1873048: add scoped retrieve perm for booking resource types

In the XUL client, when selecting a resource type, the list was limited
by owning library.  But in the web client, the list would show all
resource types across all libraries.  This commit addresses that
regression by adding a retrieve permission with context_field in the
IDL.  That way, users only see resource types owned by org units where
they have the ADMIN_BOOKING_RESOURCE_TYPE perm.

Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>