publish appsync-helper

Just stumbled upon the [AppsyncHelper](https://github.com/aws-samples/aws-appsync-resolver-samples/tree/main/examples/cdk/constructs/appsync-helper) construct which is pretty neat. Would be great to publish to npm.

Start with the AppsyncHelper construct at examples/cdk/constructs/appsync-helper and inspect how this repository structures and builds it. Determine the repository's existing package and release entry points, then verify that the construct is published as an npm package and can be installed by consumers.

Written by the indexing model from the issue text.