Better input type for unique queries

Suppose I have the following model:
```prisma
model User {
discord_id BigInt @id
steam_id BigInt?
profile_private Boolean? @default(true)
}
```
The generated graphql input query to find a unique user is of type:
```gql
input UserWhereUniqueInput {
discord_id: BigInt
}
```
This allows the user to pass a query like:
```gql
query {
user(where: {}) {
discord_id
}
}
```
Executing the above query throws an internal server error as expected.

**Solution:**
The generated input type should mark the `discord_id` field as non-nullable.

Start at generation of UserWhereUniqueInput from the Prisma User model, then trace how unique fields are rendered in the GraphQL schema. Done means discord_id is non-nullable in the generated input and an empty where object is rejected; inspect the project's generated-input coverage if available.

Written by the indexing model from the issue text.