Change check for legal part of CREATE TABLE AS SELECT ... WITH DATA plan

from a list of disallowed nodes to one of allowed nodes. Online DDL basically needs to be a vanilla table scan with filtering and projects.

Add a test for the case that brought this up.
Before we get here, we've transformed `CREATE TABLE newtab AS SELECT ... FROM oldtab WITH DATA` into `CREATE TABLE newtab(...)` and `INSERT INTO newtab SELECT ... FROM oldtab`. This rule is processing the latter for execution in the online environment.