Feature Request: Ability to specify appsync data source name for DynamoDB batch operations

As the title suggests, it would be a useful feature to be able to specify an appsync data source instead of a direct DynamoDB table name when using BatchGetItem and BatchPutItem. This would be useful to prevent table names from having to be explicitly stated in code, which makes merging development branches into production more complicated.

Start by reviewing how BatchGetItem and BatchPutItem currently accept direct DynamoDB table names and how AppSync data sources are represented. Done should mean both batch operations can use an AppSync data source name without requiring the table name to be embedded in code.

Written by the indexing model from the issue text.