[Feature]: Signers allow second DKG after specific block height

[djordon]

Feature - Signers allow second DKG after specific block height

1. Description

The signers currently allow DKG only if it hasn't run before. The change is for the signers to allow DKG a second time if it hasn't run twice and only allow a second run if the current bitcoin block height is greater than some configured block height.

1.1 Context & Purpose

We want to support full DKG. But that is difficult so we are tackling it in phases. Phase 0 was running DKG once. Phase 1 was supporting DKG a second time, and this ticket is part of phase 1.

2. Technical Details:

The current check stops the signer from participating in DKG if there exists keys in the dkg_shares table, since that indicates that DKG has succeeded. We need to change this to stop the signer from participating in DKG if the number of rows in the DKG shares table greater than 1 or if the current block height is less than the some configured block height (the one from #1199).

2.1 Acceptance Criteria:

• In TxSignerEventLoop, the signer will participate in DKG if it has never been run, or if it has run once and the current block height is greater than the one that they have "configured".

Although the above acceptance criteria mentions the configured variable, we can settle for some variable in the TxSignerEventLoop struct that gets set to whatever variable if the config work isn't done. That way we can do this task in parallel to #1199.

3. Related Issues and Pull Requests (optional):

This is related to #1199.