LiFI 7683 unlock message handler

[mpetrun5]

Create a LiFI 7683 unlock message handler that starts the signing process and returns the signature to allow for unlocking of funds on the 7683 input contract.

Implementation details

• add the lifi-7683 protocol option on the unlock API
• create the lifi 7683 unlock protocol that receives unlock data from the repayment service and signs it so the funds are received on the repayment contract

Testing details

• unit tets

Acceptance Criteria

• we are able to unlock lifi 7683 orders from the repayment service via signature