Improve documentation w/ callouts for what compute will inherit admin permissions and what access admin permissions provide

[AnilMaktala]

Describe the bug

Improve documentation w/ callouts for what compute will inherit admin permissions, and 2) what access admin permissions provide https://github.com/aws-amplify/amplify-category-api/issues/748

To Reproduce Steps to reproduce the behavior:

1. Create a GraphQL API with cognito and IAM auth.
2. create Lambda function
3. update schema with @function and field level auth rule with group access.
4. create a function and provide resource access permissions to api -> query and mutation
5. add function code to call the query containing @function

Expected behavior A clear and concise description of what you expected to happen.

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Desktop (please complete the following information):

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• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

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