[Feature]: Sign and submit complete-deposit transactions

[djordon]

Feature - Sign and submit complete-deposit transactions

1. Description

This is part of #320, but focused on complete-deposit transactions.

After we have a stacks transactions that needs signing, we need to get it signed and broadcasted.

1.1 Context & Purpose

We need to make sure that the coordinator asks the other signers to sign the transaction, add them to the transaction and the broadcast them.

2. Technical Details:

We need to hook up the TxSignerEventLoop to listen for the right messages and sign them if they are valid. For this ticket, we do not worry too much about making sure that they are valid, just that we sign them.

2.1 Acceptance Criteria:

• We can finish a full loop where we sign and broadcast complete-deposit stacks transactions that have response transactions on bitcoin.

3. Related Issues and Pull Requests (optional):

This is part of #320, and builds off of #563.