[Zod] Field with `auth()` in `@default()` should be generated as optional in zod schemas

```prisma
model User {
    id String @id @default(uuid())
    posts Post[]              
    @@allow('all', true)
}

model Post {
    id String @id @default(uuid())
    title String @default('xyz')
    userId String @default(auth().id)
    user User @relation(fields: [userId], references: [id])
    @@allow('all', true)
}
```
