[Feature]: Load the correct signer state machine when signing inputs

[djordon]

Feature - Load the correct signer state machine when signing inputs

1. Description

We currently load the state machine for the latest DKG shares. This is fine, for now, because we do not support running DKG more than once. But when we do, we need to make sure we load the correct state machine when signing a given input.

1.1 Context & Purpose

We won't provide a valid signature if we don't load the correct shares. So we need this for when we support rotate keys.

2. Technical Details:

In order to load the correct shares, we need to know the aggregate key that locks the input. That information is known to each signer when they write each sighash into their database, but it is not stored in the table. There are two options:

1. We fetch the locking public key by executing a bunch of joins.
2. We store the locking public key in the table.

Doing (1) involves a join on the dkg_shares table and the deposit_requests table. Doing (2) involves running a schema migration, doing a backfill migration, and storing the data in the table. At this time, I propose doing (2) since it is the better long term solution. In both cases the signers need to make sure that each signer loads the correct shares when we receive a sign request.

2.1 Acceptance Criteria:

• We load the correct signing shares when we get a sign request.

3. Related Issues and Pull Requests (optional):

Signing with the right aggregate key was partially addressed in #1115, this should finish it.