Feature - Remove dkg_target_rounds from DKG

1. Description

Now that we can trigger DKG when the signer set changes, the current dkg_target_rounds based DKG can be a bit messy since we may have different targets for different signers.

What we could do instead is triggering DKG if we don't have a DKG round (verified|unverified) started after the configured dkg_min_bitcoin_block_height.

Since that should make the logic lighter, we should also try to unify the coordinator and signer logic in a single place. The nuisance of it is that the signer should be more aggressive in the logging wrt the coordinator.