Consolidate "graphql_blacklisted_fields" and "exclude" directives

[chillu]

We have two mechanisms for excluding fields from model operations: graphql_blacklisted_fields on DataObject, and exclude on operations.

In the following example, both password and autoLoginHash would be excluded from the update operation on the default schema.

Member:
    graphql_blacklisted_fields:
        password: true

SilverStripe\GraphQL\Schema\Schema:
  schemas:
    default:
        models:
            Member:
                fields: '*'
                operations:
                    read: true
                    update:
                        exclude:
                            autoLoginHash: true

Wouldn't this be better placed in the global schema? Particularly if we provide a way to show the merged config tree, that's going to be a lot more transparent.

SilverStripe\GraphQL\Schema\Schema:
  schemas:
    '*':
      modelConfig:
        DataObject:
            exclude:
                password: true

SilverStripe\GraphQL\Schema\Schema:
  schemas:
    default:
        models:
            Member:
                fields: '*'
                operations:
                    read: true
                    update:
                        exclude:
                            autoLoginHash: true

[unclecheese]

I think the difference is that graphql_blacklisted_fields is a DataObject's way to declaring which fields should never be added to the schema, no matter what, across all schemas.

The exclude directive used on input types, because by default, when no fields is defined, you get fields: *, so you nee d away to override that.

It should work similarly to the standard types:

update:
  fields:
    '*': true
    autoLoginHash: false

That '*': true bit likely didn't exist when this was written.

Will remove the exclude directive from input types and the related FieldReconciler trait.

[unclecheese]

PR is here: #366

[unclecheese]

Docs are here: silverstripe/silverstripe-framework#9870