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.

首先检查 GraphQL schema 如何定义对象模型，以及 Cosmos 后端当前如何处理必需的 `id` 分区键。当开发者可以在创建 schema 时指定其他分区键（可能通过 `@partitionKey` 指令），并且 Cosmos 请求使用该定义时，此 issue 即完成。

由索引模型根据 Issue 内容生成。