pm: Store winning tickets on-disk with corresponding recipientRand value

[yondonfu]

Is your feature request related to a problem? Please describe.

While in MVS, O will submit an on-chain transaction to redeem a winning ticket immediately after receiving the ticket, it is possible that O will require the ticket data even after submitting the transaction

• The original transaction might not have been successfully broadcasted due to issues with O's Ethereum connection
• O might crash prior to the original transaction being successfully broadcasted

Beyond MVS, O might not submit an on-chain transaction to redeem a winning ticket immediately after receiving a ticket and instead choose to hold on to winning tickets to be redeemed later on.

Thus, O would benefit from being able to store winning tickets on-disk.

Describe the solution you'd like

O has a winningTickets DB table. Each table row contains all the data necessary to redeem a winning ticket on-chain: the fields of a ticket, B's signature and recipientRand (which should correspond to ticket.recipientRandHash).

When O receives a winning ticket, it stores the winning ticket data in its DB. After a winning ticket redemption transaction confirms on-chain, O can clear the relevant entry for the winning ticket in the DB.

Describe alternatives you've considered

• For MVS, we could skip DB persistence since O will always redeem winning tickets immediately, but this would leave O vulnerable to loss of funds in cases where the transaction does not confirm on-chain for some reason