Transactions in GraphQL

[arijit (Arijit Das)]

@pawan

• @transaction without any arguments starts a new transaction and returns the startTs in response headers or extensions. Also @transaction(commit: true) starts a new transaction, commits it if possible or rollbacks any mutations.
• @transaction(id: 123) executes an operation with that startTs.
• @transaction(id: 123, commit: true) commits the transaction.
• @transaction(id: 123, abort: true) aborts it.

This looks good to me, and I agree with the point mentioned for retrying. If we are supporting transactions in the query, then we should offload the retrying to the client.