Feature Request for Inheritance: ability to query and mutate with `only`

Dear Hasura,

It would be great if we could use `only` keyword for tables using inheritance.

```sql
SELECT name, elevation
FROM ONLY cities
WHERE elevation > 500;
```
Maybe something like:

```graphql
{
cities(where: {only: {_eq: true}}) {
name
}
}
```

It would be great if `update_x_by_pk` should be only by default.

Thanks for considering,

Lydia