fix: add granular read ops enum

[AaronZyLee]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:
aws-amplify/amplify-flutter#2526
Description of changes:
Add granular read operation enums in model auth operation rule
Refer https://docs.amplify.aws/cli/graphql/authorization-rules/#how-it-works

The purpose of adding enum in library is to ensure the model files generated by modelgen will be compiled. However, this is not intended for Datastore usage but for those who use modelgen files along with API plugin. It is not recommended to use them in the datastore due to the prerequisite of sync and listen. This is documented in the callout

How did you test these changes?
(Please add a line here how the changes were tested)

• Added Unit Tests
• Added Integration Tests

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #2265 (3e67d82) into main (07c0de3) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

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- Hits        11455    11451       -4     
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