Withdrawals table migration

Closes #2026 (closed)

Migrate the withdrawals table to rewards_withdrawals, so that we can replace varint user_guids, with bigints.

COPY minds.withdrawals (user_guid, timestamp, tx, amount, completed, completed_tx, status, address, gas) TO 'temp.csv';
COPY minds.rewards_withdrawals (user_guid, timestamp, tx, amount, completed, completed_tx, status, address, gas) FROM 'temp.csv';