Cascade distributed table creation via foreign key graph

The following operation fails:
```
create table ref (a int primary key, b int);
create table test (x int, y int references ref (a));
select create_distributed_table('test','x');
ERROR: referenced table "ref" must be a distributed table or a reference table
DETAIL: To enforce foreign keys, the referencing and referenced rows need to be stored on the same node.
HINT: You could use SELECT create_reference_table('ref') to replicate the referenced table to all nodes
```

Given improved support for local-reference table joins and foreign keys, we could consider taking the step suggested in the hint automatically. Optionally, via a cascade flag.