[sBTC DR] Withdrawal Flow

[stjepangolemac]

A set of functions that enables the handler to respond to new withdrawals, burn updates, fulfillment updates, and requesting broadcasting of new burn or fulfillment transactions.

It should be triggered by:

• new withdrawals
• burn status updates
• fulfillment status updates

It should be able to request these tasks:

• broadcast new burn transactions
• broadcast new fulfillment transactions

[netrome]

To make the withdrawal flow work with the bridge and be more future proof, we should look into these design issues:

stacks-archive/sbtc-docs#82
stacks-archive/sbtc-docs#31