Fix: Corrected GSI casing for generated AppSync resolvers

[nabilkem1]

Issue #: N/A or specify the issue number if applicable

Description of the Issues:

1. The global (GSI) index name referenced in the resolvers was in lowercase, while the corresponding index on the DynamoDB table was created with a capitalized name. This mismatch prevented proper data retrieval.
2. When a custom GSI index name was provided, it was correctly applied in the resolvers, but the DynamoDB table appended the sort key (SK) name to the custom index, resulting in a mismatch between the resolver configuration and the actual index name on the table.

These discrepancies caused failures when querying data, as the resolvers referenced index names that did not exist on the table.

Description of Changes:

• Normalized index naming between resolvers and DynamoDB table creation logic.
• Ensured custom index names are consistently respected and not programmatically altered during table configuration.

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