fix module imports

[cloutierMat]

part of the appsync execution rework, we lost the ability to pass in --experimental-specifier-resolution=node when executing JS code. This is probably a good thing since it could have blocked us from future versions of node.

The sad consequences is that we lost the capabilities to import without specifying the file name for rds and dynamodb.

Explicitly declaring the exports will bring about parity with aws as to how to import appsync-utils module within a user function.

// valid
import * as rds from "@appsync-utils/rds";
import { insert } from "@appsync-utils/rds";

// invalid
import * as rds from "@appsync-utils/rds/index.js";

[simonrw]

It's a shame we have to manually declare exports, however I have struggled for ages trying to get this code working across different JS implementations, and I don't understand it all so it was amazing it worked in the first place!

[cloutierMat]

Thanks for the review. Before merging, I will start a changelog in the README, similar to what we have for the airspeed library. That should enable us to properly mange versions of this library in the near future