Allow @key to reference non-required fields

[wizage]

Describe the bug
Today @key doesn't allow you to reference non-mandatory fields. This can hinder other transforms and custom revolvers that might take a null field and fill in a default if no value is given.

Amplify CLI Version
4.16.1

To Reproduce
An example:

type Answer @model @key(fields: ["owner", "gameID"])
@auth(
    rules: [
        {allow: owner, ownerField: "owner"}
    ]
)
{
    owner: String
    gameID: ID!
    answer: [Int]
}

This example, fails to compile today but should compile as the resolver will auto fill the owner field in if no value is provide due to the auth resolver.

Expected behavior
I expect a flag to be able to set in the @key transform that will allow me to disable the required non-nullable check. Or this should not stop the compile and should throw a warning letting me know that there could be possible issues down the road but will allow me to still push.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Mac
• Node Version: v12.13.1

[RossWilliams]

See duplicate aws-amplify/amplify-cli#3275

[wizage]

See duplicate aws-amplify/amplify-cli#3275

I would disagree but it does look like it does relate/might be a duplicate of aws-amplify/amplify-cli#1657