Can't configure the partition key when defining the object model

Cosmos backends require you to have a partition key of `id`, but there are many approaches to partitioning in Cosmos.

The developer should be able to define what it is when they are creating the GraphQL schema, maybe using a `@partitionKey` directive.

Start by reviewing how the GraphQL schema defines object models and how the Cosmos backend currently handles the required `id` partition key. The issue is complete when developers can specify a different partition key while creating the schema, potentially through a `@partitionKey` directive, and Cosmos requests use that definition.

Written by the indexing model from the issue text.