Bug - Set the output index in SweptWithdrawalRequests

1. Description

Right now the output index sent in accept-withdrawal-request contract calls is fixed at 2. We have the correct data in the database, we just need to set it correctly when making the contract call.

1.1 Context & Purpose

The contract call data is potentially used by users or services to properly verify that a withdrawal has been fulfilled. We should make sure that it gets set correctly.

2. Technical Details:

The contract call gets populated with data from a SweptWithdrawalRequest object, which itself gets created with the output of a query. We need to update the SweptWithdrawalRequest struct to have an output_index field and also the query to correctly populate the new field from the bitcoin_withdrawals_outputs table. Then we need to set the vout field in the returned OutPoint when calling SweptWithdrawalRequest::to_withdrawal_outpoint.

2.1 Acceptance Criteria:

• SweptWithdrawalRequest::to_withdrawal_outpoint creates the correct outpoint for the withdrawal request.

3. Related Issues and Pull Requests (optional):