sql: support column family definitions in CREATE TABLE AS SELECT

[rolandcrosby]

The new CREATE TABLE AS SELECT enhancements that @adityamaru27 is working on help with various cases when a table needs to be rewritten, including primary key changes (#20940) and other cases not handled explicitly by schema changes. Allowing a user to define column families as an additional qualifier in the table definition would be a nice improvement here, since there's not otherwise a good way to move an existing column from one family to another.