[Maintenance]: Change productType in graphql to one Type

[tjeerddie]

there is a different product graphql type, one for products that uses ProductSchema and one that is used by SubscriptionInterface that uses ProductModel (does not have relations). This should become the same Type.

[tjeerddie]

We do need the ProductModel graphql type because it is necessary for the auto registration of products to resolve correctly.

I believe the best approach is to update ProductModel to also have fixed_inputs, product_blocks and workflows, so we can add the GraphqlType ProductType to the ProductModel with ProductModel._strawberry_type = ProductType and will be resolved the same as root Products resource.