graphql/batch_executor: expose IsExpensive and IsBatch workunit fields
graphql/batch_executor: expose IsExpensive and IsBatch workunit fields

In order to tag query executions as batched or not, and expensive
or not, we expose methods on the work unit that provide this info.

samsarahq/thunder,samsarahq/thunder,samsarahq/thunder,samsarahq/thunder,samsarahq/thunder