fix(appsync): multiple interface types generates invalid schema

[BryanPan342]

Make the GraphQL Schema construct multiple interface implementation in the following manner:

type Object implements Interface1 & interface2 {
  ...
}

Fixes #10479

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[BryanPan342]

@MrArnoldPalmer @shivlaks addressing a p1 bug #10479

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• Commit ID: aadf55d
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Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).