[Bug] Lambda resolver doesn't work with any types of GraphQL fragments

Hey,

I just wanted to highlight that as a huge limitation of the approach that you have, that because of this function in Lambda:
```typescript
function createGraphqlSource(event: AppSyncResolverEvent): string {
const fieldName = event.info.fieldName
const typeName = event.info.parentTypeName
let selectionSet = event.info.selectionSetGraphQL
if (typeName === 'Mutation' && event.stash.wrapper) {
selectionSet = `{${event.stash.wrapper} ${selectionSet}}`
}

const args = fieldToArgsMap[typeName + '.' + fieldName]
if (args) {
return `${typeName.toLowerCase()}(${args.op}) {\n ${fieldName}(${args.vars}) ${selectionSet}\n}`
}
return `${typeName.toLowerCase()} {\n ${fieldName} ${selectionSet}\n}`
}
```
The line: `let selectionSet = event.info.selectionSetGraphQL` means, that due to AppSync limitations, it won't include any normal or inline fragments in that. While normal fragments can be workaround by extracting that data from `event.info.electionSetList`, inline fragments are not included there as highlighted in that issue:
https://github.com/aws/aws-appsync-community/issues/142

I believe this should be highlighted in the README, that fragments are not supported with that example and inline fragments cannot be supported with this approach in general