feat: add projection support for @index directive

[ahmedhamouda78]

Description of changes

This PR adds projection support for the @index directive in Amplify GraphQL API. The changes enable developers to specify which fields should be projected in DynamoDB Global Secondary Indexes (GSI) when using the @index directive, providing better control over query performance and cost optimization.

Key changes:

• Enhanced index directive to support projection configuration
• Updated GraphQL index transformer to handle projection parameters
• Modified resolvers to work with projected fields

CDK / CloudFormation Parameters Changed

• Added support for ProjectionType and NonKeyAttributes parameters for DynamoDB Global Secondary Indexes. Prior to this PR, the ProjectionType parameter was always set to ALL. This PR allows developers to set the ProjectionType themselves and defaults to ALL if not set, so it doesn't break backwards compatibility.
  • https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Projection.html

Issue #, if available

aws-amplify/amplify-data#604

Description of how you validated changes

• Added unit tests covering projection scenarios in amplify-graphql-index-transformer.test.ts
• Verified snapshot tests pass with updated index directive behavior
• Tested resolver functionality with projected fields in sample app

Checklist

• PR description included
• yarn test passes
• E2E test run linked
• Tests are changed or added
• Any CDK or CloudFormation parameter changes are called out explicitly

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

[svidgen]

I'm not sure offhand what is or isn't required for the AppSync/resolver side of this. But, I suspect it's more than this. I would actually kind of expect to see some new generated GraphQL types.

Sufficiently thorough e2e tests would give me some confidence this is working as expected either way though.