feat: #1200 feature signers allow second dkg after specific block height

[cylewitruk]

Description

Closes: #1200

Changes

Changes the check in the handle_wsts_message method for DkgBegin messages in the transaction signer to conditionally allow a second DKG run if:

• There has not been a DKG run yet (i.e. no entries in the signer's dkg_shares db table), OR
• If DKG has been run exactly once (one entry in the signer's dkg_shares db table) AND a DKG re-run height is configured AND the current bitcoin chain tip height is >= the configured re-run height

This copies a snippet of the config code in #1201 to be able to retrieve the config value for the DKG re-run height.

Testing Information

This currently lacks additional tests because my integration env is borked for some reason; looking into that now.

Checklist:

• I have performed a self-review of my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules