create custom input types
### Summary

Is there a simple way to create custom input types for custom mutations ?
I disabled CRUD mutations with '-insert -update -delete' default behavior, and I want to create my own.

After some experimentation, i came with this database schema :

schema.sql :
```sql
begin;

create schema exemple;
grant usage on schema exemple to exemple_anonymous;

create table exemple.email (
  address text primary key unique,
  validate_date timestamptz,
  create_date timestamptz default now()
);
comment on table exemple.email is $$
  An `Email`
$$;

grant select on table exemple.email to exemple_anonymous;

create type exemple.email_input as (
  email text
);
comment on type exemple.email_input is $$
  @behavior +insert -resource:insert
  --@behavior +insert:input:record
  --@behavior +insert -resource:insert +insert:input:record
  The input type for create_email mutation
$$;

create function exemple.create_email(
  input exemple.email_input
) returns exemple.email as $$
    insert into exemple.email (address) values (input.email) returning *;
$$ language sql strict security definer;
comment on function exemple.create_email(exemple.email_input) is $$Create an `Email`.$$;
grant execute on function exemple.create_email(exemple.email_input) to exemple_anonymous;

commit;
```

Postgraphile produces multiple types :
- type `EmailInputRecord` to avoid potential conflict with `EmailInput` from table exemple.email I suppose (I don't need this)
- input `EmailInputRecordInput` documented as 'An input for mutations affecting EmailInputRecord' (this is the one I need)

Is it possible to tell Postgraphile to use `exemple.email_input` directly as an input type named `EmailInput` and to use its description as documentation for this input type (eg. 'The input type for create_email mutation' here) ?

The behavior 'insert:input:record' seems promising, but it seems that I don't understand how it should work.

### Additional context

Postgraphile :  5.0.0-beta.11
Postgres : 15.4
Node : 20.5.1

Postgraphile defaultBehavior : '-insert -update -delete'
