Table Function Foreign Key not working
Postgraphile version: 4.11.0

### Summary

I can't get a table function to nest properly. I tried using a `@foreignKey` smart comment on the FUNCTION as well as on the TYPE that the function returns.

### Background

Hello, I am trying to extend the example from here: <https://www.graphile.org/postgraphile/relations/>

It has 2 tables: `person` and `post`.

Here they are, copied from the above link (but placed in the same schema):

```sql
create table person
(
    id         serial primary key,
    name       varchar not null,
    about      text,
    email      varchar not null unique,
    created_at timestamp default current_timestamp
);

create table post
(
    id        serial primary key,
    headline  text not null,
    body      text,
    -- `references` 👇  sets up the foreign key relation
    author_id int4 references person (id)
);

create index on post (author_id);
```

This is the command line I am using:

    $ postgraphile -c postgres://test1 --enhance-graphiql

I can get all people, together with the posts of each person with this GraphGL query that works great:

```gql
{
  allPeople {
    nodes {
      name
      email
      postsByAuthorId {
        nodes {
          headline
          body
        }
      }
    }
  }
}
```

### Problem: Table Function with Foreign Key

Now I want to add a PostgreSQL Table Function so that I can search for posts using a string:

```sql
create type person_search_posts_type as (
    id int4,
    headline text,
    body text,
    author_id int4
);

create function person_search_posts(search TEXT)
    returns setof person_search_posts_type
as
$function$
    select id,
           headline,
           body,
           author_id
    from post
    where headline ILIKE ('%' || search || '%')
$function$ language sql stable;
```

This is the GraphQL query I would now like to write:

```gql
{
  allPeople {
    nodes {
      name
      email
      personSearchPosts(search: "dog") {
        nodes {
          headline
          body
        }
      }
    }
  }
}
```

I tried this smart comment, which does not work:

```sql
COMMENT ON FUNCTION person_search_posts IS '@foreignKey (author_id) references person (id)';
```

This one doesn't work either:

```sql
COMMENT ON TYPE person_search_posts_type IS '@foreignKey (author_id) references person (id)';
```

What do I need to do so that my desired GraphQL query will work?

Thank you