API (GraphQL) category does not have relational model CRUD guidance

[david-mcafee]

Describe the content issue: A clear and concise description of what the content issue is. Is there content missing or is there incorrect content?

Unlike DataStore, the API (GraphQL) category does not offer any guidance on how to create / read / update / delete relational models. I noticed this when attempting to reproduce the following issue: https://github.com/aws-amplify/amplify-js/issues/11079

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[AnilMaktala]

We have recently revamped our docs. Please refer to this section of the docs?.