fix(introspection): primary key info when pk is belongsTo field

[AaronZyLee]

The introspection schema will generate a primaryKeyInfo for each model intermediate representation. It is not correctly retrieved when the following conditions are met:

• the primary key is the belongsTo connection field(targetName)
• The feature flag value respectprimarykeyattributesonconnectionfield is set to false

This will trigger the code block and remove the pk field from the representation
https://github.com/aws-amplify/amplify-codegen/blob/main/packages/appsync-modelgen-plugin/src/visitors/appsync-visitor.ts#L1023-L1039

Description of changes

Add condition check to block the execution of field removal for that scenario

Issue #, if available

Fix aws-amplify/amplify-category-api#1399

Description of how you validated changes

yarn test
amplify-dev codegen model-introspection --output-dir .

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• Breaking changes to existing customers are released behind a feature flag or major version update
• Changes are tested using sample applications for all relevant platforms (iOS/android/flutter/Javascript) that use the feature added/modified

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

[phani-srikar]

Please include some context in the PR description as it is not clear from the title what this is accomplishing.

[phani-srikar]

What are the other targets that are valid here and why this fix only required for "introspection" target?

[AaronZyLee]

The other targets are controlled by the feature flag value. For introspection, there are cases where the app has CPK value as false and the code block above is entered. That's why it is protected not to execute the line when target is introspection and belongsTo connnection field is primary key