unify getTableDescriptors() and listTableDescriptorsByNamespace()

currently we have getTableDescriptors()/listTableNames()
and listTableDescriptorsByNamespace()/listTableNamesByNamespace()
which are just filtering by namespace.

The first two are already able to filter tables by regex,
and there is also an ACL check which shows only the table the user have access to,
while the namespace version just return a list without any ACLs check.

to me there is no point to keep the *ByNamespace() version on the server side,
since the "base" version must be able to do the filtering by
namespace and the ACLs check must be the same for both anyway.
or at least we can just call the base version with the ns filtering.