[the-overmind] Support HP withdrawals

Summary:
Need to have withdrawals for onchain actions to make any sense. Add support.

Limit to 1 per user per 24 hrs to prevent abuse (e.g. calling it all the time for the sats).

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19337