Say which sites an asset category exists at. An empty list clears this category's own rule,
Asset configuration
Say which sites an asset category exists at. An empty list clears this category's own rule,
which is not the same as offering it everywhere: a category that states no rule follows the nearest category above it that states one, and is unrestricted only when nothing above it states one either.
Replaces the whole list in one call, the same shape as api.set_type_scope: the caller sends what should be true now, not a delta.

