Field level auth on a customType

**Describe the bug**
`a.customType()` currently allows users to set authorization on fields, but when this is deployed no resolver is created and no error is displayed.

**To Reproduce**
```typescript
const schema = a.schema({
Post: a.customType({
id: a.id().required(),
title: a.string().required(),
// I would expect this field to have a resolver and to be omitted if not logged in
description: a.string()
.authorization((allow) => allow.authenticated()),
}),

searchForPosts: a
.query()
.arguments({
search: a.string(),
})
.returns(a.ref('Post').required().array().required())
.handler(
a.handler.function(defineFunction({
entry: './posts/search.ts',
}))
),

})
.authorization((allow) => allow.publicApiKey());
```

**Expected behavior**
Either:
- (Preferred) An appropriate field resolver to be created, and for the field to be null when not authorized.
- (Less preferred) Not able to call `.authorization` on a customType

**Desktop (please complete the following information):**
- "aws-amplify": "6.15.3",

**Additional context**
Switching `.customType` to `.model` causes the resolver to be created (but also creates a db table that are unnecessary)

Reproduce the schema in the issue, including the searchForPosts entry point at posts/search.ts, and inspect the deployed behavior for authorization on the customType.description field. Compare this with the resolver behavior when the type is changed to a model. Done means the chosen authorization behavior is enforced without requiring an unnecessary database table.

Written by the indexing model from the issue text.