Support `import foreign schema` for wrappers with static schema.

[imor]

Enhancement

Describe the enhancement

For foreign data sources like Stripe which have a fixed schema (as opposed to something like Airtable where the user can create any schema) support import foreign schema statement.

Additional context

This will make is easy for users to create all foreign tables by writing something like:

import foreign schema stripe_schema
from server stripe_server into stripe;

Instead of manually specifying tables like:

create foreign table stripe.accounts (
  id text,
  business_type text,
  country text,
  email text,
  type text,
  created timestamp,
  attrs jsonb
)
  server stripe_server
  options (
    object 'accounts'
  );

See FDW routines for import foreign schema.