nakamoto: not work with signet network

[vincenzopalazzo]

While using Nakamoto as the fallback client is a good option for core lightning, there is an option where we are going
to set the signet network.

Nakamoto return an error, and I was not able to get enough logs, but
I guess that there are no signet nodes in the DNS? or simply the block
not exist and there is a bug inside folgore

This require more research!