R1:6c9026c33a45

Allow ModularTransactions to opt in to providing data to Conduit

Summary:
Ref T5873. See PHI14. I don't want to just expose internal transaction data to Conduit by default, since it's often: unstable, unusable, sensitive, or some combination of the three.

Instead, let ModularTransactions opt in to providing additional data to Conduit, similar to other infrastructure. If a transaction doesn't, the API returns an empty skeleton for it. This is generally fine since most transactions have no real use cases…