Add details to custom auth: Multi-user data access

**Describe the content issue**:

I have been working on adding authentication to our application and I feel like there should be some more details about how the multi-user data access is managed.

Does the owner field have to be added to the query? How do we add an owner to the entry once created? What if we create a new user that needs to be added as an owner of multiple (nested) entries via custom (Lambda) function? Does this work out of the box with the `@searchable` directive? There are a few generalized questions on the integration with Amplify that seem to be helpful to add to the public docs.

Ideally, having a pointer to a sample repo with some detailed comments on the functionality would be awesome, but I understand that this is a relatively big ask.

I have used [this repo](https://github.com/carlos-jmh/large-project/blob/main/amplify/backend/function/addUserToHouseHold/src/index.js) as inspiration to set up my auth rules, using custom graphQL authorizer. However, I am running into difficulty setting up the `list...` and `search...` query authorizers, and think that having more documentation on the multi-user access would help me understand whether I need to write a custom auth strategy or depend on multi-user access as is.

**URL page where content issue is**: https://docs.amplify.aws/javascript/build-a-backend/graphqlapi/customize-authorization-rules/#multi-user-data-access